PURPOSE: To prevent a working attachment from interfering with a vehicle body with simple structure by installing a proximity sensor and a detected piece, respectively fitted to two constituents turned to bend around one pin connecting part, in the positions of the same distance from the pin axis of the pin connecting part.

CONSTITUTION: The operating lever 28 of an hydraulic remote control valve 27 for an arm is operated in the direction of an arrow mark (a) from a neutral position N to turn the arm 12 of the working attachment 10 in such a way as to be pulled toward the ventral side of a boom 11, and when the bending angle of the arm 12 to the boom 11 reaches a specified limit angle θ, a proximity sensor 20 detects a detected piece 21. In response to a detection signal, a controller 36 switches a solenoid change-over valve 33 into a tank communicating oil passage position B and a pilot change-over valve 29 for the arm into the neutral position. As a result, arm pulling operation of making the bending angle of the arm 12 smaller than the limit angle θ is stopped so as to hinder the working attachment 10 from interfering with a vehicle body.