Provided is a mechanical sealing device which is simply configured and wherein a rotation ring can be stably held in a specified axial position, and warping of the sealed surfaces can be prevented, thereby making it possible to obtain appropriate sealing characteristics. In a mechanical sealing device, a rotation ring is axially held between a rotation ring locking surface of a sleeve and a rotation ring locking surface of a collar. Furthermore, the sleeve, the rotation ring fixing collar, and the rotation ring are integrated together by means of a baffle knock pin for the rotation ring. Due to the above, whether positive pressure or negative pressure is applied, the rotation ring does not move, nor do the sealed surfaces of the rotation ring become warped. Moreover, assembly can be simply performed only by means of the knock pin.