Abstract: An end surface-contact mechanical seal providing a shielding seal between a liquid area (A) and an atmospheric area (B) by a relative rotation, while in a contact state, of opposing end surfaces (4a, 6a) of a case-side sealing ring (4), which is fixed to a seal case, and a ceramic shaft-side sealing ring (6), which is held on the sleeve (22) of a rotary shaft (2). A rubber O-ring (5) is installed between a sealing ring-side seal surface (63a), which is formed on the inner peripheral surface of the shaft-side sealing ring (6), and a shaft-side seal surface (22c), which is formed on the outer peripheral surface of the sleeve (22), so as to be relatively movable in the axial direction while sealing the surfaces. A diamond film (14a) is formed over the entire surface of the sealing ring-side seal surface (63a).