To allow to govern a torque variation in a wide area from a low rotation to a high rotation, in a constitution to transmit the motive power from an engine to running wheels through a transmission device.

In a transmission shaft on the way of a motive power transmitting passage to transmit the motive power of an engine to running wheels through a transmission device, the transmission shaft is divided in an engine side shaft 64 and a running wheel side shaft 65, both shafts are provided on the same axial center, and a fixed body 64a and a sliding body 58 are provided opposing on the shafts of the connecting part of the engine side shaft 64 and the running wheel side shaft 65. A cam groove 58a to engage a steel ball 56 with a steel ball 54b is provided at the abutting part of the fixed body 64a and the sliding body 58, so as to energize the sliding body 58 to the fixed body 64a side, and at the same time, a thrust regulating means of engine is connected and interlocked to the sliding body 58.