Abstract: A tool clamping device for clamping a tool on a main spindle or releasing the same from the main spindle, which includes: a main spindle rotatably supported on a headstock; a push rod extended through the spindle hole of the main spindle so as to be axially slidable, urged rearward by a weak spring and capable of being moved axially for fixing a tool to or releasing the same from the main spindle; a clamping spring for pressing the push rod rearward; a sleeve disposed contiguously with one end of the clamping spring so as to be movable relatively to the push rod; a first interlocking mechanism formed between the push rod and the sleeve so as to interlock the sleeve with the push rod when the sleeve moves in a direction to allow the expansion of the clamping spring and to release the sleeve from the push rod when the sleeve moves in a direction to compress the clamping spring; a second interlocking mechanism capable of being disengaged by the movement of the push rod in a direction to compress the clamping spr