To provide a hydraulic circuit capable of working well without increasing any hydraulic circuit to be installed in a cabin anew or without making hydraulic piping works for the cabin and allowing the operator to manage with a hands-on operation system.

The hydraulic circuit is equipped with a pilot direction selector valve 3 connected with a hydraulic cylinder 2 of a hydraulic attachment according to the invention and furnished at its two sides with pilot circuits, a main pump 4, a left shuttle valve 5a, a right shuttle valve 5b, a solenoid proportional decompression valve 6, a stamping pedal type operation valve 7, a pilot pump 8, a controlling amplifier 9 where an at-hand operation switch 10 to make manual manipulation is connected inside the cabin of a construction machine and which controls the decompression valve 6 in conformity to the command given by the at-hand operation switch 10, and the at-hand operation switch 10 to perform manual manipulations.