To operate a large-sized control valve and plural control valves with good accuracy even by a small pilot valve in a working machine provided with the pilot valve for outputting pilot pressure corresponding to the operating amount of an operating tool, and a pilot operated control valve for controlling the supply of pressure oil of an actuator.

A pilot oil passage for supplying pilot oil pressure to a first and second control valves 6, 7 for a boom is provided with a pressure control valve 21 operated by pilot pressure output from the pilot valve 19 for the boom to output a large flow of pilot pressure oil at the pressure equal to the output pressure from the pilot valve 19 for the boom to the first and second control valves 6, 7 for the boom.