We studied a method to obtain the relationship between the temperature and heat storage characteristics of PCM mixed building materials. While the temperature of heat plates, which were put on both sides of the specimen, were changing at a constant speed, the temperature of the specimen and the amount of heat flow to the specimen were measured respectively. Relationships between temperature and specific enthalpy were obtained from measured values, and the relationship between temperature and specific heat (apparent specific heat including latent heat of composite material) was obtained. Then, latent heat, phase change temperature region, and peak temperature of phase change could be calculated. For this measurement method, we compared differences of measurement results when the heat capacity of the specimen and the temperature change condition were changed. Measurement of ASTM C 1784 was also conducted, and the measurement results were compared and examined. The results of this measurement method were influenced by measurement conditions that temperature change range and measurement range, but roughly the same as those of ASTM method.