Three types of moisture diffusion coefficient measurements were performed on thin-film samples of epoxy resin, and the measured values and measurement times were compared. The manual measurement according to JIS K 7209 took more than 100 days, while the measurement time of the vapor adsorption analyzer was 15 days and that of the differential pressure water vapor transmission rate analyzer was 2.1 days. The moisture diffusion coefficient and saturated water absorption obtained by the vapor adsorption analyzer were in general agreement with the manual measurement. On the other hand, the moisture diffusion coefficient obtained by the differential pressure water vapor transmission rate analyzer was in general agreement with the manual measurement, but the saturated water absorption calculated by the solution–diffusion mechanism was different from the manual measurement.