Abstract: In order to provide a check valve capable of sufficiently suppressing the mixing of air into the container even if a certain impact is applied to the container and also capable of stably maintaining good pouring of the content, a check valve 10 of the invention is formed of rubber material and manufactured by integral molding. The check valve 10 has a tubular main body 1 having openings 1a and 1b at opposite ends, a lid 3 arranged to close one opening 1a of the main body 1, and a hinge 5 that connects the main body 1 and the lid 3. The lid 3 has a projection 3a on the side surface 3b, the projection 3a coming in contact with a peripheral edge of the opening 1a of the main body 1.