PURPOSE: To make the structure of a device simple and compact and reduce an operation load by forming a conical face portion and an annular face portion on a clutch outer while forming a conical face portion on a clutch inner and forming an annular face portion on a brake plate.

CONSTITUTION: A conical face portion 45 centering around a crank shaft 7 and an annular face portion 47 which is bent in a direction perpendicular to the crank shaft 7 from the outer periphery of the conical face portion 45 are formed on a clutch outer 33. A conical face portion 59 which is frictionally engageable with the conical face portion 45 is formed on a clutch inner 31. Also, an annular face portion 69 which is frictionally engageable with the annular face portion 47 is formed on a brake plate 35. Thereby, the structure can be made simple and compact, preventing the stoppage of an engine at the time of engaging/disengaging a clutch and, further reducing an operation load.