PURPOSE: To make it possible to prevent the outflow of fuel or operating fluid with simple operation in advance in the case a circuit has to be opened for maintenance and inspection, etc., and to stop quickly the outflow of fuel or operating fluid in the case the circuit is damaged.

CONSTITUTION: Opening and shutting valves 22a, 22b, 22c and 22f respectively to an outlet and a returning port of a fuel tank 2 and an operating fluid tank 6, opening and shutting valves 22e and 22f to the front and rear of a tuning motor 11, opening and shutting valves 22g and 22h to the front and rear of a running motor 12, opening and shutting valves 22i and 22j to the front and rear of a boom cylinder 13, opening and shutting valves 22k and 22m to the front and rear of an arm cylinder 14, opening and shutting valves 22n and 22o to the front and rear of a bucket cylinder 15, and opening and shutting valves 22p and 22q are provided to the front and rear of an oil cooler 17. Opening and shutting valves 22a-22q are capable of opening and shutting operation by switching operation of control switches 23a, 23b,... provided to an operation room.