To dispense with a flow dividing valve to simplify the circuit and reduce the cost by connecting together the hydraulic circuit of a front wheel clutch and the hydraulic circuit of a PTO cluth in parallel to a hydraulic pump for common use.

In front of a hydraulic pump 65, a front wheel drive selector valve 63 changing over oil feed to hydraulic clutches 16, 17 as the front wheel clutches of a front wheel drive device 39 and a PTO selector valve 66 changing over oil feed to a PTO clutch 22 are arranged on the upper face of a transmission case 5. In the hydraulic circuit controlling the respective hydraulic clutches 16, 17 and the PTO clutch 22, the discharge side of the hydraulic pump 65 is connected to an oil passage 64, the passage is branched into two directions from the oil passage 66, the one is connected to the pump port P1 of the front wheel drive selector valve 63, the other is connected to the pump port P2 of the PTO selector valve 66, and they have the hydraulic pump 65 for common use.