To improve the life of a chain guide by reducing the frictional force of part of a chain applied to the guide surface of the chain guide.

A rear arm 12 is pivotally supported on a body frame 3 via a pivotal support means 14, and rear wheels 9 are supported on the rear arm 12. An endless chain 31 is disposed to connectively interlock the rear wheels 9 with a drive means 23 supported on the body frame 3. The pivotal support means 14 comprises bearings arranged on a pivotal axis 13 to pivotally support the front end of the rear arm 12 on the body frame 3. A chain guide 49 has a top surface used as a guide surface and supports part of the chain 31 located above the pivotal support means 14 so that the part is slidably rested along the guide surface. The front end of the chain guide 49 is supportably fitted on part of the pivotal support means 14. The part of the pivotal support means 14 is deviated from the bearings axially on the pivotal axis 13.