In a three phase inverter device, a smoothing capacitor, a bus bar at a positive electrode side and a bus bar at a negative electrode side are formed on a first surface of the circuit substrate. Electronic components containing a microcomputer, etc., a differential wiring pattern, a single wiring pattern and a current wiring pattern are formed on a second surface of the circuit substrate. A ground pattern is formed in the inside of the circuit substrate in order to separate the electronic components, the differential wiring pattern, the single wiring pattern and the current wiring pattern from the smoothing capacitor, the bus bar at the positive electrode side and the bus bar at the negative electrode side.