Sealing member, method of manufacturing the same, pressure adjustment mechanism, liquid ejection head, and liquid ejection apparatus

Provided is a sealing member to be used as a valve in a pressure adjustment mechanism. The sealing member includes a base member having high strength, and has high reliability. The sealing member includes an elastic member (valve portion) having an annular abutment portion (valve distal end portion) formed as an annular protrusion and the base member (lever portion). When a held portion having a tubular shape extending from the annular abutment portion is held in an annular groove formed in the base member, the elastic member is fixed to the base member. A holding length over which an annular groove holds the held portion along a depth direction of the base member is set longer than a width of the annular groove.