{Technical Problem} To provide a mechanical seal, either of two seal rings thereof providing a function of a slide bearing, in which rattling in the radial direction on a bearing part is reduced as much as possible by eliminating the need for axial movement of the seal ring used also as the slide bearing, and replacement of the seal rings are facilitated. {Solution to Problem} A mechanical seal which is housed in a seal cavity formed between a housing 1 and a rotating shaft 2 and which seals between the housing 1 and the rotating shaft 2, is characterized in that the mechanical seal comprises a stationary side seal ring 20 and a rotating side seal ring 21 in opposed sliding contact with the stationary side seal ring 20, one seal ring 20 of the stationary side seal ring 20 and the rotating side seal ring 21 is disposed on a sealed fluid side and constitutes a slide bearing which supports the rotating shaft 2, the other seal ring 21 is disposed on the opposite side to the sealed fluid side, and a pressing member 25 is attached to the other seal ring 21 for biasing the other seal ring 21 in the axial direction to press sealing faces of both the seal rings.