A clutch mechanism of the power device includes a movable gear member which is rotated integrally with a wheel and engaged with a stationary gear member when moved in a first direction and disengaged from the stationary gear member when moved in a second direction opposite to the first direction, an armature for pushing out the movable gear member in the first direction when rotated relatively to the movable gear member, and an electromagnetic coil for applying brake resistance to the armature by attracting the armature by the magnetic force to restrict a co-rotating state of the armature and the movable gear member. The armature has a clutch holding surface for maintaining a clutch-engaged state where the movable gear member and the stationary gear member is engaged with other even when the electromagnetic coil is turned off in the clutch-engaged state.