Engine automatic stop and start device and engine automatic stop and start process

In an automatic idling stop system, a meshing engagement between a pinion gear and a ring gear is achieved quickly and quietly, while a motor rotates by inertia. There is provided an apparatus for automatically stopping an engine when an automatic stop condition is satisfied, and restarting the engine after that, when a restart condition is satisfied, the apparatus comprising: a ring gear (12) which is to be coupled to a crankshaft of the engine; a starter motor (14) for starting the engine; a pinion gear (16) for transmitting rotation of the starter motor to the ring gear; a pinion gear moving means (17) for moving the pinion gear by energization to bring the pinion gear into meshing engagement with the ring gear; and a starter control means (11) for controlling a to be applied to the pinion gear means of tension, so that it falls within a predetermined range, when the pinion gear and the ring gear are brought into meshing engagement by movement of the pinion gear and the pinion gear moving means.