Bipedal walking models with compliant legs have been used to describe the ground reaction forces (GRFs) of human. In previous research, it was observed that leg stiffness of bipedal walking model with damped compliant leg increased with speed to get the maximum forward propulsion, taking resonance characteristic by selecting oscillation period correlated well with the duration of single support phase. In this study, we tuned the model of bipedal walking with damped compliant leg to match human GRFs for loaded subjects and compared it with that of the unloaded subjects. Seven subjects walked without load and with load at three different gait speeds, which were decided by their self-selected speed and their maximum speed. Leg stiffness of the model for loaded subjects increased with speed and was larger than that of the model for the unloaded subjects. Leg stiffness normalized by body and load weight, however, was not changed as compared with leg stiffness for unloaded subjects which was normalized by body weight. It means that human with load behaves as heavy human without load. The loaded model also may select stiffness which has oscillation period correlated well with the duration of single support phase to get the maximum forward propulsion. This result implies that leg stiffness normalized by total weight is decided by gait speed.