PURPOSE: To provide a temporary clamping state in a clamp device of a tool holder furnished with a cylindrical shaft part by bringing a ball into contact with a wedge surface of the cylindrical shaft part with pressure with proper force by pressing a sleeve on the side of the ball by a pressing means.

CONSTITUTION: When a clamp cone 7 is moved in the direction of a main spindle central line, a ball 3 makes contact with a wedge surface of the clamp cone 7 and is moved outward in the radial direction of a cylindrical shaft part la while guided by a cylindrical guide member 4, pushed on the wedge surface of an inner peripheral surface of the cyclindrical shaft part 1a by required force, a tool holder 1 is pulled to a shank hole 2a, and a clamping state is formed. In the meantime, when the clamp cone 7 is moved in the reverse direction, the ball 3 can move inward in the radial direction of the cylindrical shaft part 1a, but as the wedge surface of a sleeve 19 constantly presses the ball 3 outward in the radial direction of the cylindrical shaft part 1a by force of a spring 20, wedge work grows between the ball 3 and the wedge surface of the cylindrical shaft part 1a, and the tool holder 1a is thereby temporarily clamped.