The purpose of the present invention is to provide a mechanical seal having consistent sealing performance achieved while the durability is maintained. A mating ring (120) is provided with: a slide section (121) having a slide surface sliding on a seal ring (110) and located on the atmosphere (A)-side end surface of the slide section (121) in the axial direction of a shaft (200); and a section (122) to be held, the section (122) extending in the axial direction toward fluid (F) to be sealed, from the radially outer end of the slide section (121) and being held by a sleeve (130). The mating ring (120) is provided affixed to the sleeve (130) and is further provided with an annular holder (500) subjected to pressure applied by an O-ring (140) which is subjected in the axial direction to the liquid pressure (P) of the fluid (F) to be sealed, the fluid (F) having flowed into a space formed by the flange section (132) of the sleeve (130) and the section (122) to be held of the mating ring (120).