PURPOSE: To attain miniaturization of a total unit and decrease of weight of an axle driving gear by arranging an HST type transmission in a case of connecting half-split upper/lower cases, and by interposing, between an oil hydraulic pump and motor of constituting the HST type transmission, an oil path plate of connecting an oil path between both the hydraulic pump and motor.

CONSTITUTION: By connecting half-split upper/lower cases 1, 2 vertically divided in a horizontal direction, a transmission case is constituted, and between horizontal connection surfaces of both the cases 1, 2, a pair of right/left axles and a motor shaft 5 are journalled. A counter shaft is arranged between the motor shaft 5 and a pair of the right/left axles, and from the motor shaft 5 through the counter shaft, power is transmitted to a ring gear of a differential gear interposed between a pair of the right/left axles. An HST type transmission, comprising an oil hydraulic pump P and motor M, is arranged on an extension line of the motor shaft 5, and by an oil path formed in an oil path plate 3 to which the oil hydraulic pump P and motor M are fixed, oil paths of both the pump and motor P, M are connected.