A current detection circuit (4) detects a device current flowing in the semiconductor device (1). A voltage detection circuit (5) detects a device voltage applied to the semiconductor device (1). A temperature calculation device (6) has a table collecting device temperatures of the semiconductor device (1) respectively corresponding to plural collector currents and plural collector voltages, and reads out a device temperature corresponding to the device current detected by the current detection circuit (4) and the device voltage detected by the voltage detection circuit (5) from the table.