In an apparatus for estimating a temperature of a heating element such as IGBT mounted on an electronic printed circuit board, a first temperature and a second temperature at positions away from the heating element are detected, and it is determined whether a cooling device is operative. The temperature of the heating element is estimated based on the first and second temperatures using a first equation when the cooling device is inoperative, whereas it is estimated using a second equation when the cooling device is operative, thereby enabling to accurately estimate the temperature of the heating element equipped with the cooling device.