To ensure a sealing property, i.e., a reverse flow preventing property, to make an operability of a valve element good, to set a flow characteristic to the optimum condition and to effectively exhibit a reverse flow prevention pressure resistant property.

The valve element 1 opens/closes a flow passage by contacting/ leaving with a valve seat 3 formed on a body 6. This valve element 1 is a valve element for a check valve constituted by a surface layer 2 closely contacted with the valve seat 3; and an encroaching preventing part, provided on an inner layer part of this surface layer 2, for preventing that the surface layer 2 is encroached to the valve seat.