To provide a check valve having a relatively simple structure, a comparatively simple assembly work of a valve element, and a good versatile structure.

The check valve 10 is equipped with a valve seat 11 and valve element 12 approximately in a disc shape, and the valve seat 11 has a periphery 11a formed flat and an inside part 11b furnished with a shaft hole 11c to admit penetration of a shaft and a distribution hole 11d to allow a fluid to flow through. The valve element 12 has the shaft 12a to penetrate the shaft hole 11c and a valve body 12b approximately in a disc shape formed at one end of the shaft 11c and having a size as covering the distribution hole 11d in the valve seat 11 when viewed in the axial direction. The check valve 10 is arranged inside a tee 22b in the condition that the periphery 11a of the valve seat 11 is pinched by a socket 26 of the tee 22b and a spigot 24 of an elbow pipe 22a.