An engine starting device for an idling-stop vehicle, for stopping an engine upon satisfaction of a predetermined idling-stop condition during idling of the vehicle, comprising: - a ring gear to be connected to a crank shaft of the engine; - a starter motor unit comprising a starter motor, a pinion gear for transmitting rotation of the starter motor, and a pinion gear connection means for causing the pinion gear to mesh with the ring gear; and - a starter control section for controlling the starter motor unit, wherein the starter control section (1,3) energizes the starter motor to cause the starter motor to rotate upon satisfaction of a predetermined starter motor rotation start condition prior to clearing of the idling-stop condition in response to a restart request after the satisfaction of the idling-stop condition, and causes the pinion gear to mesh with the ring gear to be connected thereto by the pinion gear connection means upon satisfaction of a predetermined pinion gear meshing condition; characterized in that the engine starting device further comprises a ring gear rotation speed detecting means for detecting a rotation speed of the ring gear (Nr), wherein the starter motor rotation start condition is that the rotation speed of the ring gear (Nr) becomes equal to or less than a first predetermined value (Nb) after the satisfaction of the idling-stop condition (Step S310), wherein the first predetermined value (Nb) is a rotation speed at which the engine can be started by fuel re-injection, and the pinion gear meshing condition is that the rotation speed of the ring gear (Nr) becomes less than a second predetermined value (Na) (Step S30), wherein the second predetermined value (Na) is a sum of a steady-state value of the rotation speed of the starter motor with an input voltage and a difference (Ne) in rotation speed between the ring gear and the pinion gear at which the ring gear and pinion gear can mesh with each other. - a ring gear to be connected to a crank shaft of the engine; - a starter motor unit comprising a starter motor, a pinion gear for transmitting rotation of the starter motor, and a pinion gear connection means for causing the pinion gear to mesh with the ring gear; and - a starter control section for controlling the starter motor unit, wherein the starter control section (1,3) energizes the starter motor to cause the starter motor to rotate upon satisfaction of a predetermined starter motor rotation start condition prior to clearing of the idling-stop condition in response to a restart request after the satisfaction of the idling-stop condition, and causes the pinion gear to mesh with the ring gear to be connected thereto by the pinion gear connection means upon satisfaction of a predetermined pinion gear meshing condition; the engine starting device further comprises a ring gear rotation speed detecting means for detecting a rotation speed of the ring gear (Nr), wherein the starter motor rotation start condition is that the rotation speed of the ring gear (Nr) becomes equal to or less than a first predetermined value (Nb) after the satisfaction of the idling-stop condition (Step S310), wherein the first predetermined value (Nb) is a rotation speed at which the engine can be started by fuel re-injection, and the pinion gear meshing condition is that the rotation speed of the ring gear (Nr) becomes less than a second predetermined value (Na) (Step S30), wherein the second predetermined value (Na) is a sum of a steady-state value of the rotation speed of the starter motor with an input voltage and a difference (Ne) in rotation speed between the ring gear and the pinion gear at which the ring gear and pinion gear can mesh with each other.