Abstract: A hydraulic circuit construction for a working vehicle operable as a backhoe and also as a dozer, the circuit construction comprising a multiplex valve assembly with a dozer control valve for a dozer system, a motor control valve for one of right and left running systems, and an arm confluence valve for supplying pressure fluid to an arm cylinder of a backhoe system from a pump common to the dozer and motor valves are connected in series with one another to the pump, and a change-over valve is provided downstream from the dozer and the motor valves and upstream from the arm confluence valve for interrupting the supply of the pressure fluid from the pump to the arm confluence valve. The above circuit construction enables the vehicle to perform both operations, namely a bulldozing operation without the vehicle being urged to run obliquely, and a successful running out operation from a marshy ground by an arm operation without any one of the running system being urged to stop by the work load of the arm.