A tool post for a machine tool comprising: a supporting member that movably supports a tool ; a driving force transmission part that is disposed between the supporting member and the tool to transmit driving force to the tool , the driving force transmission part comprising an engaging member that is located in a side of the supporting member , and an engaging member that is located in a side of the tool , and the engaging members engaging in accordance with a movement of the tool , at least one of the engaging members provided to be biased to an engaging posture in which both of the engaging members are capable of engaging; and a releasing member that is disposed between the side of the tool and the side of the supporting member , and releases the engaging posture by pressing the engaging member against a biasing force, wherein a driving force is transmitted to the tool via the driving force transmission part by moving the tool to a predetermined position where the both of the engaging members engage, and wherein the releasing member is disposed to release the engaging posture a first by pressing engaging member in the middle of the movement of the tool toward the predetermined position, the first engaging member being biased to the engaging posture when the first engaging member is in a disengaging state, and wherein the releasing member is disposed to release the pressing when the tool reaches the predetermined position in which both of the engaging members engage, characterized in that a groove is the engaging member that is located in a side of the supporting member a tenon shaped protrusion is the engaging member that is located in a side of the tool , wherein the releasing member is two protrusions, wherein the two protrusions are positioned in the vicinity of the both sides of the tenon shaped protrusion along the turning direction of a turret , and wherein the tip surfaces of the respective protrusions protrude further than the tip surface of the tenon shaped protrusion . a supporting member that movably supports a tool ; a driving force transmission part that is disposed between the supporting member and the tool to transmit driving force to the tool , the driving force transmission part comprising an engaging member that is located in a side of the supporting member , and an engaging member that is located in a side of the tool , and the engaging members engaging in accordance with a movement of the tool , at least one of the engaging members provided to be biased to an engaging posture in which both of the engaging members are capable of engaging; and a releasing member that is disposed between the side of the tool and the side of the supporting member , and releases the engaging posture by pressing the engaging member against a biasing force, wherein a driving force is transmitted to the tool via the driving force transmission part by moving the tool to a predetermined position where the both of the engaging members engage, and wherein the releasing member is disposed to release the engaging posture a first by pressing engaging member in the middle of the movement of the tool toward the predetermined position, the first engaging member being biased to the engaging posture when the first engaging member is in a disengaging state, and wherein the releasing member is disposed to release the pressing when the tool reaches the predetermined position in which both of the engaging members engage, characterized in that a groove is the engaging member that is located in a side of the supporting member a tenon shaped protrusion is the engaging member that is located in a side of the tool , wherein the releasing member is two protrusions, wherein the two protrusions are positioned in the vicinity of the both sides of the tenon shaped protrusion along the turning direction of a turret , and wherein the tip surfaces of the respective protrusions protrude further than the tip surface of the tenon shaped protrusion . <EOS>