A drive pulley is formed in a cup-like shape one end side of which is integrally formed with a peripheral wall in a cylindrical shape, the peripheral wall in the cylindrical shape of the drive pulley is formed with openings to be engaged with a ratchet member at intervals of 90 degrees along a circumferential direction, an engaging face for engaging with the ratchet member is formed at a side edge of each for the openings directed in an engine starting direction, and a side edge opened substantially orthogonal to the engaging face or by an angle equal to or larger than 90 degrees is formed at a side edge of the opening on an opposed side opposed to the engaging face.