To provide a highly reliable engine starting device which has a configuration including a one-way clutch in a ring gear, can be manufactured economically and constrains distortion accompanying heat treatment from occurring.

In the engine starting device, a clutch inner 41 can perform heat treatment for enhancing abrasion resistance and fatigue strength resistance on a ring gear 2a formed on a first rotor 2 and the clutch inner 41 separately because it is formed in substantially ring-like shape distinct from the first rotor 2 and is attached on outer periphery of a cylindrical inner retention 2b provided on the first rotor 2. Thus, it is possible to manufacture economically without performing waste heat treatment on unnecessary portion in the first rotor 2. In addition, it becomes also unnecessary to perform surplus process for eliminating distortion without damaging clutch function and causing abnormal sound generation because of being constrained distortion accompanied with heat treatment from occurring in the first rotor 2.