A machine tool having a frame, a turret head rotatably mounted upon the frame, at least one tool spindle rotatably supported within the turret head, first coupling means mounted upon the tool spindle, and second coupling means slidably and rotatably mounted within the frame and adapted to engage with the first coupling means of the tool spindle positioned at an operative position so as to transmit a driving power to the tool spindle. Within the turret head there is mounted angular maintenance means for maintaining the tool spindle in a first predetermined angular position. Within the frame there are mounted release means for releasing the tool spindle positioned at the operative position from the angular maintenance means, orienting means for positioning the second coupling means to a second predetermined angular position, and means for moving the second coupling means positioned at the second predetermined angular position into and out of engagement with the first coupling means.