A mechanical seal configured to seal a fluid moving towards an outside-diameter side from an inside-diameter side of sliding faces where a stationary ring and a rotating ring slide against each other, the stationary ring being configured to be fixed to a stationary wall with a bellows interposed therebetween, the mechanical seal comprising: the bellows having an inner cylindrical part, an outer cylindrical part formed with a greater outer diameter than that of the inner cylindrical part, and a curved part connecting the inner cylindrical part and the outer cylindrical part; a case member (223; 228; 238) having a cylindrical wall part (223a; 228a; 238a) extending in an axial direction, an accommodating part (223b; 228b; 238b) comprising a case wall (223c, 228c, 238c) that extends outward in the radial direction from one end of the inner cylindrical part (223a, 228a, 238a) and that is formed over the entire periphery, an outer cylindrical part (223d, 228d, 238d) that extends in the axial direction from an outside- diameter-side end part of the case wall (223c, 228c, 238c) and that is formed over the entire periphery, and an outer end part (223e, 228e, 238e) that extends to an end part of the outer cylindrical part (223d, 228d, 238d) and that is formed into a thin-walled part, and a wall part (223g; 228g; 238g) provided with a groove part (223f; 228f; 238f) at the other end of the cylindrical wall part (223a; 228a; 238a); a holding member (224; 229; 239) having a protruding part (224a; 229a; 239a); and an outer gap part provided on the outside-diameter side of the curved part of the bellows to absorb deformation of the curved part, and wherein the outer cylindrical part of the bellows is configured to be held on the stationary ring by the accommodating part (223b; 228b; 238b) of the case member (223; 228; 238), and the inner cylindrical part of the bellows is configured to be held on the stationary wall by the holding member (224; 229; 239), wherein the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) is formed over an entire periphery; and the groove part (223f; 228f; 238f) of the case member (223; 228; 238) engages with the protruding part (224a; 229a; 239a) of the holding member (224; 229; 239), and the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) and the holding member (224; 229; 239) have an overlapping portion (Lp) in the axial direction over the entire periphery, whereby the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) covers the curved part of the bellows and the outer gap part over the entire periphery. the bellows having an inner cylindrical part, an outer cylindrical part formed with a greater outer diameter than that of the inner cylindrical part, and a curved part connecting the inner cylindrical part and the outer cylindrical part; a case member (223; 228; 238) having a cylindrical wall part (223a; 228a; 238a) extending in an axial direction, an accommodating part (223b; 228b; 238b) comprising a case wall (223c, 228c, 238c) that extends outward in the radial direction from one end of the inner cylindrical part (223a, 228a, 238a) and that is formed over the entire periphery, an outer cylindrical part (223d, 228d, 238d) that extends in the axial direction from an outside- diameter-side end part of the case wall (223c, 228c, 238c) and that is formed over the entire periphery, and an outer end part (223e, 228e, 238e) that extends to an end part of the outer cylindrical part (223d, 228d, 238d) and that is formed into a thin-walled part, and a wall part (223g; 228g; 238g) provided with a groove part (223f; 228f; 238f) at the other end of the cylindrical wall part (223a; 228a; 238a); a holding member (224; 229; 239) having a protruding part (224a; 229a; 239a); and an outer gap part provided on the outside-diameter side of the curved part of the bellows to absorb deformation of the curved part, and wherein the outer cylindrical part of the bellows is configured to be held on the stationary ring by the accommodating part (223b; 228b; 238b) of the case member (223; 228; 238), and the inner cylindrical part of the bellows is configured to be held on the stationary wall by the holding member (224; 229; 239), wherein the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) is formed over an entire periphery; and the groove part (223f; 228f; 238f) of the case member (223; 228; 238) engages with the protruding part (224a; 229a; 239a) of the holding member (224; 229; 239), and the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) and the holding member (224; 229; 239) have an overlapping portion (Lp) in the axial direction over the entire periphery, whereby the cylindrical wall part (223a; 228a; 238a) of the case member (223; 228; 238) covers the curved part of the bellows and the outer gap part over the entire periphery.