To provide a power unit for a small vehicle constituted to reinforce the support rigidity of a kick spindle while covering the greater part of a change mechanism.

In this power unit for small vehicle wherein at least a part of the change mechanism C is disposed on one side of a crankcase 11, a side cover 20 for accommodating a portion, exposed outside the crankcase 11, of the change mechanism C is detachably jointed to one side wall of the crankcase 11, and the kick spindle 21 is supported to the side cover 20 and the crankcase 11. A kick arm 22 is stuck to the outer end part, projecting outside the side cover 20, of the kick spindle 21.