A flywheel 2 and an HST unit 5 are accommodated in a flywheel housing 13 of a working vehicle, the HST unit 5 comprising an oil hydraulic motor 9, an oil hydraulic pump 10, an oil hydraulic circuit block 17 containing an oil hydraulic circuit therein and supporting one end of an oil hydraulic motor shaft and one end of an oil hydraulic pump shaft, and a cover housing 18 secured to the oil hydraulic circuit block to cover the oil hydraulic motor and the oil hydraulic pump and support the other end of the oil hydraulic motor shaft and the other end of the oil hydraulic pump shaft; the oil hydraulic circuit block 17 being secured to an intermediate housing connected to the flywheel housing 13.