An apparatus for starting an engine, including a motor, an output shaft driven by the motor, a pinion provided along the output shaft, and an electro-magnetic solenoid device. The electro-magnetic solenoid device is configured to push the pinion axially toward a ring gear of the engine to mesh the pinion with the ring gear and transfer a rotational force, which is referred to as a motor torque, generated by energization of the motor from the pinion to the ring gear, thereby starting the engine. The apparatus is configured such that, at starting of the engine in its warmed-up state, the motor torque can continue to be applied from the pinion to the ring gear until at least the second compression stroke even when an engine speed varies.