END SURFACE CONTACT TYPE MECHANICAL SEAL

PROBLEM TO BE SOLVED: To provide an end surface contact type mechanical seal for exhibiting the excellent seal function even in any of normal operation time and back pressure operation time.SOLUTION: This end surface contact type mechanical seal: includes a fixed sealing ring (2) fixed to a seal case and a movable sealing ring (6) movably held by a rotary shaft (3) via a spring holding ring (4) and an O ring (5); has a relationship of d1D1, 0.15≤(d2-d1)/(D2-D1)≤0.85 and 0.95≤(d1+d2)/(D1+D2)≤1.05 among an inner diameter D1 and an outer diameter D2 of relative rotation sliding contact parts of both sealing rings (2 and 6), a diameter d1 of a first seal surface (43a) and a diameter d2 of a second seal surface (65a); and is constituted so that the balance ratio becomes 0.6-0.9 in any of a case where a first fluid region (A) has higher pressure than a second fluid region (B) and a case where the second fluid region (B) has higher pressure than the first fluid region (A).