PURPOSE: To prevent malfunction of an air tool preliminarily by installing a control lever interlocked with a handle of a cock member of an air supply hose for closing the cock member when the air tool is moving up so as to stop supply of air automatically when it is not used but kept stand-by at an upper position by energizing force of a balancer.

CONSTITUTION: An air tool (a stapler, for example) W suspended to be moved up and down by a balancer 1 through a suspending member 3 is moved down against the energizing force of the balancer 1 when it is used, and a control lever 13 is manually operated to open a cock member 12 of an air supply hose 11 to supply air to the air tool W for use. When the air tool W is not used, the air tool 1 is moved up by the energizing force of the balancer, and the cock member 12 is closed by the control lever 13 installed freely slidably to the suspending member 3 corresponding to the up motion, thereby air supply to the air tool W is stopped automatically to prevent malfunction of the air tool W.