A capacitor connected to a microcomputer voltage wiring is downsized. A series regulator on an electronic control unit for automotive includes a battery as an in-vehicle power supply, a relay, an input side capacitor, a series regulator circuit, and an output side capacitor, and is connected to a microcomputer. The series regulator circuit includes an n-channel MOSFET, a gate voltage regulator circuit as an output control circuit of an FET, and a gate voltage holding capacitor. A capacitor GND voltage (gate voltage) is adjusted by the gate voltage regulator circuit to convert an input side capacitor voltage into an output side capacitor voltage, and supply a microcomputer current to the microcomputer.