A life estimation circuit includes a temperature detector configured to detect temperature of a power element unit, an inflection point detection unit configured to detect an inflection point of temperature variation in the power element unit based on an output signal from the temperature detector, an operation unit configured to determine an absolute value of a difference between the temperature of the power element unit at an inflection point detected this time and the temperature of the power element unit at an inflection point detected last time, a count circuit configured to count the number of times that the absolute value of the difference in temperature has reached a threshold temperature, and a signal generation unit configured to output, when a count value from the count circuit reaches a threshold number of times, an alarm signal indicating that the power element is about to reach the end of its life.