An electricity supply device that reduces a delay in starting an engine. A vehicle includes a starter motor for starting an engine, a start magnet making and breaking connection between the starter motor and a battery, a fuel pump, and a control unit controlling fuel injection and ignition timing of the engine. An electricity supply device of the vehicle includes: a main relay making and breaking connection between a load of the vehicle, the load not including the starter motor, the start magnet, and the battery; a clutch switch connected to the battery, and set in a conducting state when a clutch lever is gripped; a start switch connected between the clutch switch and a coil of the start magnet; and a diode allowing a current to flow from a point of connection between the clutch switch and the start switch to a coil of the main relay.