To directly transmit power between a motor shaft and an axle by means of gears in a HST type axle driving device while an intermediate reduction gear train is eliminated.

A hydraulic pump P and a hydraulic motor M are set up in the inside of a mission case for an axle driving device formed out of an upper part case 2, and of a lower part case 1, the hydraulic pump P and the hydraulic motor M are mounted to an oil passage body 3, a hydraulic transmission means is provided, in which the delivery capacity of the hydraulic motor M is greater than the delivery capacity of the hydraulic pump P, and it is so constituted that the reduction in speed can be accomplished through the hydraulic transmission means and one set of mechanical gears.