A power-storage-type engine starting system includes a coil spring (48) for storing power to be used in starting the engine. A shaft end (31a) of a crankshaft (31) is configured to pass through a cylindrical shaft part (42a) and is passed through a one-way clutch (51) attached to inside of an assist boss (47) so that an assist boss and the one-way clutch can be provided at radially outside of the shaft end, whereby the crankshaft is made shorter.
