The in-vehicle controller of the present disclosure is installed in a vehicle together an engine, a motor capable of generating electricity connected to a crankshaft of the engine, a high voltage battery connected to the motor by a high voltage power line, a low voltage battery, a DC/DC converter connected to the high voltage power line and a low voltage power line connected to the low voltage battery, and a relay attached to the high voltage battery side of the high voltage power line from the DC/DC converter. The in-vehicle controller of the present disclosure stops driving the DC/DC converter after driving off the motor when completing the batteryless driving by disconnecting the high voltage battery with the relay turned off.