A rotation shaft seal disposed between a housing and a rotation shaft, and provided with a seal member of rubber having a lip end portion which extends as to diminish in diameter to a fluid storing chamber side, wherein the lip end portion has a contact portion which contacts a surface of the rotation shaft and an end face which is facing the rotation shaft, and a concave portion, generating a component of force in diameter direction to raise the lip end portion outward in the diameter direction when receiving pressure in the fluid storing chamber, is formed on the end face.