The present invention promptly and quietly brings a pinion gear into mesh with a ring gear during inertia rotation of an engine in an automatic idling stop system. Disclosed is a device that automatically stops an engine when an automatic stop condition is met, and then restarts the engine when a restart condition is met, the device provided with: a ring gear (12) connected to a crankshaft of the engine; a starter motor (14) for starting the engine; a pinion gear (16) transmitting rotation of the starter motor to the ring gear; a pinion gear moving means (17) for moving the pinion gear with an applied current to bring the same into mesh with the ring gear; and a starter control means (11) for controlling such that a voltage applied to the pinion gear moving means is in a predetermined range, when the pinion gear is brought into mesh with the ring gear by moving the pinion gear with the pinion gear moving means.