Abstract: The invention relates to a power transmission mechanism between an engine starting device and an engine. A side surface shape of a lever-shaped engaging and disengaging member (107) in a side facing to a ratchet wheel (120) of a rotation driven portion is formed in a concave shape concaved in a direction away from the wheel (120). The lever-shaped engaging and disengaging member (107) is engaged with and disengaged from a centrifugal clutch mechanism of the engine engaging with and disengaging from the ratchet wheel (120). A first engaging and disengaging lever (141) is engaged with the ratchet wheel (120), a sufficient force to start the engine is accumulated in a force accumulating power spring (131), thereafter the engagement of the first engaging and disengaging member (141) is disconnected by a manual operation, and the ratchet wheel (120) is rapidly rotated by releasing the accumulated force in the force accumulating power spring (131).