Complex heat capacity obtained in melting region of polymer crystals by temperature-modulated differential scanning calorimetry of heat flux type has been calibrated with a method based on a model proposed by Hatta. The calibration method corrects for the effect of thermal conductivity of the DSC apparatus on the magnitude and phase angle of the heat capacity. The validity of the correction has been confirmed by examining the reversible melting and crystallization of indium under quasi-isothermal conditions. For the irreversible melting of polymer crystals analyzed with an additional underlying heating rate, the calibrated heat capacity becomes a complex quantity with a frequency dependence roughly approximated by Debye's type, the characteristic time of which depends on the underlying heating rate. This behavior qualitatively agrees with the previous results obtained by the calibration of baseline-subtraction from the phase angle. The applicability of the "baseline-subtraction" has also been discussed.