A rubber gasket is interposed between opposing two members in a state of being held in a fitting groove formed in one of two members, and includes a concave surface located in a central area in a width direction thereof and extending in a circumferential direction thereof, and seal beads located on both sides of the concave surface in the width direction thereof. The concave surface and the seal beads are formed in each of a surface of the rubber gasket facing a bottom surface of the fitting groove and a surface of the rubber gasket facing the other of two members. Assuming that a maximum depth of the concave surface is D, and a height between the seal beads facing the bottom surface of the fitting groove and the seal beads on an opposite side thereto is A, the expression D=0.025A˜0.075A (1) is satisfied.