An engine start device includes a generator, a battery charged by the generator, a starter, an electric double layer capacitor and a DC/DC converter. The electric double layer capacitor is connected between the starter and the battery. The DC/DC converter has an input terminal connected to the battery and the electric double layer capacitor. The DC/DC converter has an output terminal connected to the starter and the electric double layer capacitor. According to voltage of the battery, internal DC resistance of the battery or internal DC resistance of the electric double layer capacitor, the DC/DC converter effects control of charge voltage of the electric double layer capacitor so as to stabilize voltage applied to a starter motor and stabilize the engine start.