To study first-order phase transitions, we applied temperature-modulated calorimetry. Especially, in this paper, we carried out the measurements using two kinds of calorimeters, a light-irradiation type AC calorimeter and a temperature-modulated differential scanning calorimeter. The former is useful to obtain the detailed behavior of heat capacity near a first-order phase transition but not the magnitude of latent heat. On the other hand, the latter is useful to obtain the magnitude of latent heat. in a further study on the kinetic mechanism (nucleation, phase boundary motion, etc.) in a hybrid region composed of the mixture of two states associated with low- and high-temperature phase, it is very important to consider the results obtained from the calorimetric measurements which an done under small amplitude of modulated temperature and a wide range of frequency based upon the detailed structure of the hybrid region.