A tool holding device for machine tool, which comprises a circular arrangement of a number of collet fingers (5) received in a spindle hole (12) of a spindle (1) and capable of turning between a clamp position where a knob (22) of a tool holder (2) is clamped and an unclamp position where the knob is released, a collet sleeve (6) surrounding the circular arrangement of collet fingers to constrain turning thereof, an air cylinder for moving the collet sleeve relative to the collet fingers in the axial direction of the spindle to release constraint on turning of the collet fingers, a first coned disk spring (43) for providing a great force to draw the knob toward the spindle through the collet fingers, an air cylinder for removing a drawing force of the first coned disk spring, and a second coned disk spring (46) for providing a force to maintain the collet fingers at the clamp position against the weight of the tool holder even when turning of the collet fingers is allowed and a drawing force of the first spring is removed.