A tool unclamping device has a motor (1); a rotating shaft (3) connected to the motor (1); a cam (4) provided at the rotating shaft (3); a power transmission member (5) axially movable when pressed by the cam (4) and having a recess (5a) at the center in the radial direction of the member; a frame (10) provided surrounding the power transmission member (5); a support member (12) inserted in the power transmission member (5) in its radial direction and fixed to the frame (10); an elastic member (7) placed in the recess (5a), located between the power transmission member (5) and the support member, and urging the power transmission member (5) to the motor (1) side; and an output shaft (15) driven by power from the power transmission member (5) and bringing a tool (25) to an unclamping state.
