A check valve (1, 2, 3, 4, 5, 6, 7, 8) comprising: a housing including an inlet channel, a valve chest, and an outlet channel; a seat member provided around the inlet channel, the seat member including a seat portion; a valve element (20, 80) pressed against the seat portion (14, 18) to close the inlet channel and including a valve head portion (21, 81) located under a sealing portion, a spring receiving portion provided at a lower portion of the valve head portion (21, 81) and projecting in a radial direction, and a columnar portion smaller in diameter than the valve head portion (21, 81) provided under the spring receiving portion; a spring configured to push the valve element (20, 80) toward the seat portion (14, 18); a guide portion provided at the housing and configured to guide the valve element (20, 80) when the valve element (20, 80) moves in an axial direction; and a damper chamber communicating with the valve chest through a space between the valve element (20, 80) and the guide portion, the damper chamber being configured to attenuate axial moving force of the valve element (20, 80), wherein: the spring is arranged in the valve chest; characterised in that the cross-sectional area of the damper chamber is 90% to 100% of the pressure receiving area of the valve element (20, 80), which is the cross-sectional area of the seat portion (14, 18); and the maximum compression ratio of the volume of the damper chamber is two or more. a housing including an inlet channel, a valve chest, and an outlet channel; a seat member provided around the inlet channel, the seat member including a seat portion; a valve element (20, 80) pressed against the seat portion (14, 18) to close the inlet channel and including a valve head portion (21, 81) located under a sealing portion, a spring receiving portion provided at a lower portion of the valve head portion (21, 81) and projecting in a radial direction, and a columnar portion smaller in diameter than the valve head portion (21, 81) provided under the spring receiving portion; a spring configured to push the valve element (20, 80) toward the seat portion (14, 18); a guide portion provided at the housing and configured to guide the valve element (20, 80) when the valve element (20, 80) moves in an axial direction; and a damper chamber communicating with the valve chest through a space between the valve element (20, 80) and the guide portion, the damper chamber being configured to attenuate axial moving force of the valve element (20, 80), wherein: the spring is arranged in the valve chest; characterised in that the cross-sectional area of the damper chamber is 90% to 100% of the pressure receiving area of the valve element (20, 80), which is the cross-sectional area of the seat portion (14, 18); and the maximum compression ratio of the volume of the damper chamber is two or more. the spring is arranged in the valve chest; characterised in that the cross-sectional area of the damper chamber is 90% to 100% of the pressure receiving area of the valve element (20, 80), which is the cross-sectional area of the seat portion (14, 18); and the maximum compression ratio of the volume of the damper chamber is two or more.