PURPOSE: To decrease a shock, at the time of connecting a clutch, while contriving the simplification of constitution and the cost down by providing a multi-disk friction-type clutch mechanism in a high speed side gear train while constituting a shift mechanism of a ball-type clutch.

CONSTITUTION: A shift mechanism 46 has a ring unit 45, and a pressing surface 45a, for pressing steel balls 33, 41, and an escape surface 45b, for retracting the steel balls 33, 41, are formed in the internal peripheral surface of the ring unit 45. A streak of circumferential groove 50 is formed in the peripheral part of the ring unit 45, a pin 52 is engaged with this groove 50, a turnable pivotally supporting pin 54 is provided in a case 9, an arm 55 is secured to a lower part of the pin 54 and the pin 52 is secured to the end part of the arm 55. A lever 56 is operated, when the pivotally supporting pin 54 is turned, the ring unit 45 is moved in the axial direction, and the pressing surface 45a presses the steel balls 33, 41 to perform high-low speed selection. While friction plates 29 and 30, brought into press contact by a belleville spring 31, are provided in a high speed gear train 60, and a shock is absorbed at the time of connecting a clutch.