A tool clamping device for multiple-operation machines or machining centers. The device has a self-blocking fork for selectively securing a tool on a tool changing device or autooperator, the fork being in the shape of jaws which partially embrace the shank of a tool. In both arms of the fork there are profile grooves in which there are located pivotally mounted blocking pins. Between the blocking pins and the bottom wall of the grooves there are springs for constantly pressing the blocking pins toward their blocking position. The blocking pins are L-shaped, and in their blocking position the end of one arm of each protrudes outwardly in position to be engaged by the face keys of the spindle of the machine in the operation of removing a tool from the spindle of the machine.