An engine control unit which can solve current leakage from an ignition system or the like due to attachment of water drops or the like when washing a vehicle. A power circuit receiving power supply from a battery, supplying the power to an engine control unit, and maintaining supply of a power to the engine control unit even when the power supply from the battery is stopped, a unit disconnection detecting circuit for detecting that the engine control unit is disconnected from the battery, and an EEPROM are provided, and when disconnection of the engine control unit is detected, an engine stop flag is stored in the EEPROM, and when the engine control unit is connected and a power is supplied from the battery, the engine is not permitted to start for a certain period of time if the engine stop flag is stored in the EEPROM.