The purpose of this study was to develop work clothes, with shoulder protectors, that provide optimal operability over a range of working postures for construction workers. The study method for the development of work clothes is as follows. First, 102 construction workers were questioned about the actual condition in which the construction work clothes were worn. Next, workers at a reinforced-concrete construction site were filmed performing their daily tasks and the video was analysed using the OWAS technique to identify postures commonly used during their routine work. The analysis was used to identify postures routinely used by construction workers. Then, in a detailed interview-based questionnaire, three workers at the construction site were asked to adopt working postures and to identify the most uncomfortable parts of their work clothes. The workers repeated the same process in experimental clothes cut along the horizontal and vertical directions of the uncomfortable parts. Then, they were asked to bend the waist by 90° and bend the knees by 120°, and the cuts were scanned in three dimensions during this process and analysed. The analysis was used to design prototype work-clothes to maximize construction-worker operability in the range of postures. The study method for the development of shoulder protector for work involving carrying loads on the shoulder was as follows. First, the shape and fit of two types of commercial shoulder protectors were analysed. Next, three prototype model shoulder protectors with shoulder point height as the variable were developed. Then, the prototypes were analysed in three dimensions for fit and durability. The analysis was used to design a final 3D-printed prototype shoulder protector. Finally, the prototype work clothes and shoulder protector were developed as final products after subjective and objective evaluation and feedback. The results of the study were as follows. First, it is important to note that unlike managers, who received most of their work clothes from the company, construction workers were only supplied with vests. Consequently, the construction workers were wearing work clothes they personally purchased. In the survey, the workers noted that good activity, safety, and protection were important buying criteria for work clothes but it was difficult to find optimal work clothes. Thus, it was necessary to develop and provide suitable work clothes for workers. Second, the results of analysing the work postures of general worker, wood worker, transport worker, and iron workers in the reinforced-concrete construction site are as follows. General workers took a wide variety of postures through the day. Wood workers had large variability in back and leg motion. The iron workers had considerable bending of both the waist and the leg. The transport workers usually carried heavy rebar on their shoulders without wearing shoulder protectors. Among these workers, the rebar-placement and fixing-workers required the development of comfortable work clothes most urgently because they had the longest working time in a fixed posture. Further, a need was identified for the transport workers to wear shoulder protectors because their work entailed many working postures that caused high stress to the musculoskeletal system. Third, in the in-depth interviews, the respondents noted that they felt discomfort in their backs, upper arms, thighs, knees, and hips as a result of their primary work. Fourth, prototypes incorporating elastic bands in the uncomfortable parts of the commercial work clothes were developed and tested. Based on the feedback received during prototype testing, the elastic band was applied in both vertical and horizontal directions and arranged in a continue line at 6.0 cm intervals. Moreover, an elastic band was placed in areas where the skin was most stretched during body motion. The developed work clothes were designed in a single pattern by connecting the armhole line of the back and the sleeve armhole line such that the elastic band on the back was extended to 5.0 cm to the armhole part. The resulting wearing comfort of the arm was excellent. The ease for each part of the developed workwear is as follows: chest circumference (34.4 cm), upper-arm circumference (20.5 cm), back length (31.1 cm), hip circumference (34.8 cm), thigh circumference (23.8 cm), and knee circumference (23.8 cm). Fifth, the shoulder protector was developed by using a three-dimensional human body shape and making space close to the side-neck and shoulder points. In other words, the shoulder point was raised vertically 1.0 cm from the side-neck point of the human body. The shoulder point was raised 2.0 cm in the vertical direction from the human body, and the shoulder center line length was specified at 14.5 cm. The area of the shoulder protector was specified at 10.0 cm to the back and 7.0 cm to the front, based on the shoulder line. The designed shoulder protector had a large area of contact with heavy objects, low stress due to the load, good durability, and low pressure. Further, the shoulder protector did not shift out of the shoulder position in the operating posture; therefore, it was comfortable to wear. Two construction workers evaluated the designed work clothes and shoulder-protector in a field simulation and judged it to be more comfortable than the commercial work clothes. The results of this study are expected to be used as basic data for the future workwear market.