A device for starting an engine includes a starter for starting the engine and an ECU. The starter includes a pinion gear for engagement with a ring gear for cranking the engine, an actuator structured to engage the pinion gear with a ring gear, and a motor for rotating the pinion gear. The actuator and the motor can individually be controlled. The ECU has a rotation mode for driving the motor prior to drive of the actuator and an engagement mode for causing the actuator to engage the pinion gear and the ring gear with each other prior to drive of the motor. When a request to start the engine is made, the ECU switches selection between the rotation mode and the engagement mode based on a rotation speed of the engine and a reduction rate in rotation speed of the engine.