Temperature rise in semiconductor switching element that is part of a power conversion device is estimated to assess the degradation and remaining lifetime of the switching element. This is accomplished with a heat generation amount calculation unit in a calculation processor, where current command values Id* and Iq* and voltage command values vu*, vv* and vw* are used to calculate a chip loss. Current values iu*, iv* and iw* of all output phases are estimated from the current command values. The ON/OFF loss of the chip is represented by a function of an estimated value for a current flowing in each output phase, and the loss can be derived by integration with a PWM carrier frequency f. With respect to a conduction loss, a conduction time is integrated with the estimated current value and a saturation voltage, which is a function of the estimated current value.