Abstract: An engine starting device includes an ignition switch configured to cause turning-on and off of a main power source line connecting a power source for a vehicle and an engine control unit (ECU). The ignition switch includes a stationary contact and a movable contact that is rotatable relative to the stationary contact. The stationary contact includes a main contact configured to be connected to a power source input section of the ECU and a starter contact configured to be connected to a starter. The engine starting device also includes a relay provided on a sub power source line that is connected in parallel to the main power source line, the relay connecting the power source of the vehicle and a sub power source input section of the ECU, the relay being excited by the start of the ECU and providing electric continuity between the power source and the ECU.