To adjust the speed change ratio over a wide range with simple constitution by arranging a speed change mechanism to change speed of rotation of the hydraulic pump side and the hydraulic motor side and a speed change ratio control device to adjust both swash plate angles of a hydraulic pump and a hydraulic motor.

Respective swash plate angles are adjusted by operating moving sleeves 153 and 155 by guide grooves 149 and 151 for a hydraulic pump 33 and a hydraulic motor 35 formed on a shift column 139. Relative rotation is generated between a pump swash plate 39 and a pump cylinder block 41 to receive a load by rotation of an input shaft 5, and high oil pressure is generated in a cylinder 69 of a pump piston 43 pushed down by the pump swash plate 39. Low oil pressure is generated in the cylinder 69 of the pump piston 43 pushed back to the pump swash plate 39 by a piston ring 45, and the oil pressure of the cylinder 69 is imparted to a pushing-out side cylinder 83 of the hydraulic motor 35 through a high pressure side oil passage. A motor piston 55 moves in the rotational direction along a swash plate angle of a motor swash plate 51, and rotates a motor cylinder block 53 and an output shaft connected to this.