A check valve (1) for a through hole in a compartment wall (100) comprises an elastic membrane (20) covering an open end (16) of a flow passage (14), a base (11) to which the elastic membrane (20) is fixed, and a protector (30) covering at least a portion of the elastic membrane (20), wherein the elastic membrane is fixed to the base in a state where it is elastically stretched over and forced against a sealing surface (17) surrounding the open end (16) so as to seal the flow passage (14). The elastic membrane lifts from the sealing surface when the pressure in the flow passage is high. The elastic membrane may be air- or gas-permeable and, preferably, waterproof so as to impart a low pressure venting functionality to the check valve.