In order to assess the reliability of Korean raingage, called “Chukwookee”, measured precipitation amounts during the period of Yi-Dynasty, we have examined transient variabilities in the time series of annual and monthly percipitation values from Korean raingage and also from conventional modern raingages. The data employed for analysis are the monthly and annual amounts of precipitations and the monthly number of precipitation days. There does not exist any significant differences in the monthly mean precipitation amounts between by Korean raingage and by conventional raingages. Monthly number of precipitation days is almost complete except a few intermittent discontinuities before 1775. There exist very clearly distinguished abrupt increases of the monthly number of precipitation days around 1720 and 1907. We are not able to give a reasonable explanation for the former discontinuity. But the latter seems to be attributed to the change of unit in measuring precipitation amounts. Such a change in the time series of monthly number of precipitation days does not have any significant effect on the monthly precipitation amounts. Precipitation amounts are relatively conservative compared with the precipitation days. There are no abrupt changes such as found in the time series of the monthly number precipitation days. But there observed two suppressed precipitation periods around the years of 1770 and 1900, separately. In contrast with the changes in the number of precipitation days, we have not found any significant relationships between any of these changes in the time series of the monthly precipitation amounts and a change of the unit employed in precipitation measurement. When comparing the Korean raingage measured precipitations with the equivalent precipitation amounts reproduced from the modern conventional raingages measured precipitations for the period from 1943 to 1991 by taking into account the unit of scale used in measuring precipitation amount, we have recognized that in Seoul the precipitation days are very sensitive to the unit of scale for the measurement but the precipitation amounts are not. So we are led to conclude that Korean raingage measured precipitations could be used for the study of climatic changes in the precipitation amounts of Seoul without adopting an ad hoc correction scheme as tried before.