To simply discriminate whether some other movable valve element is operated or not even if a specified movable valve element is operated.

A passage 56 is provided extending from a pilot hydraulic pump 51 to a tank 58. In the passage 56, a logic circuit spool part 48a of an attachment spool 48 which is put in the communicating state in the neutral position and in the throttled state in the selecting position, and logic circuit spool parts 39a, 41a, 44a, 46a of front working machine system spools 39, 41 44, 46 which are put in the communicating state in the neutral position and in the passage cutoff state in the selecting position are provided in series. A pressure detector 62 for detecting the change of pressure is provided on the upstream side of the logic circuits spool parts 39a, 41a, 44a, 46a, 48a, whereby the operation of the attachment spool 48 is discriminated according to low pressure produced in the throttle state, and the operation of the front work machine system spools 39, 41, 44, 46 is discriminated according to high pressure produced in the passage cutoff state.