An inverter ECU is applied to a hybrid vehicle having an engine and a motor generator as drive power source and a motor generator control system. A drive control part generates drive signals for an inverter based on torque request to the motor generator. A temperature information acquiring part acquires an element temperature value and a cooling water temperature value as an inverter temperature value. An abnormality detection part detects whether the inverter temperature value is within a diagnosable temperature range, and performs abnormality detection for the motor generator control system when the inverter temperature value is within the diagnosable temperature range. When the inverter temperature value is not placed within the diagnosable temperature range, the energy supplied to the inverter is adjusted to move the inverter temperature value into the diagnosis allowable temperature range to correctly perform the abnormality detection.