A fixing device of a workpiece in a machine tool comprising: a fixing section configured to rotate with a main spindle , fix the workpiece in a closed state, and release the fixation of the workpiece in an open state; an actuating lever configured to rotate with the main spindle , and be displaced to open and close the fixing section ; a sliding member which is provided to be movable between a first position (P1) and a second position (P2) along an axis direction of the main spindle , and configured to rotate with the actuating lever while displacing the actuating lever when the sliding member is in contact with the actuating lever in the second position (P2) in the movable range; a rotation transfer member which is disposed to have contact with the sliding member in the first position (P1) in the movable range of the sliding member , and configured to rotate with the main spindle , wherein the sliding member is configured to loosely engage with the main spindle in a rotatable manner and to rotate with the rotation transfer member when the sliding member has contact with the rotation transfer member in the first position (P1) in the movable range of the sliding member , wherein the sliding member , the rotation transfer member and the actuating lever are disposed or formed such that the sliding member does not have contact with both of the rotation transfer member and the actuating lever at least in a partial range between the first position (P1) and the second position (P2) of the sliding member , and wherein the sliding member thereby rotates in asynchronization with the main spindle , and contacts the actuating lever in a phase different from that of the rotating main spindle , characterised in that , the rotation transfer member is made of an elastic member, is elastically deformed by contact with the sliding member in the first position (P2), and rotates the sliding member by a friction force resulting from an elastic force by the elastic deformation. a fixing section configured to rotate with a main spindle , fix the workpiece in a closed state, and release the fixation of the workpiece in an open state; an actuating lever configured to rotate with the main spindle , and be displaced to open and close the fixing section ; a sliding member which is provided to be movable between a first position (P1) and a second position (P2) along an axis direction of the main spindle , and configured to rotate with the actuating lever while displacing the actuating lever when the sliding member is in contact with the actuating lever in the second position (P2) in the movable range; a rotation transfer member which is disposed to have contact with the sliding member in the first position (P1) in the movable range of the sliding member , and configured to rotate with the main spindle , wherein the sliding member is configured to loosely engage with the main spindle in a rotatable manner and to rotate with the rotation transfer member when the sliding member has contact with the rotation transfer member in the first position (P1) in the movable range of the sliding member , wherein the sliding member , the rotation transfer member and the actuating lever are disposed or formed such that the sliding member does not have contact with both of the rotation transfer member and the actuating lever at least in a partial range between the first position (P1) and the second position (P2) of the sliding member , and wherein the sliding member thereby rotates in asynchronization with the main spindle , and contacts the actuating lever in a phase different from that of the rotating main spindle , characterised in that , the rotation transfer member is made of an elastic member, is elastically deformed by contact with the sliding member in the first position (P2), and rotates the sliding member by a friction force resulting from an elastic force by the elastic deformation. <EOS>