To provide a gas check valve, which can be arranged in any facing and whose cracking pressure, knocking noise and chattering noise are low.

A valve guide tube 5, which includes a gas passing hole 5b for outflowing gas inflown through a port 1 to the gas downstream side chamber 3 side, is provided on the gas outflow chamber 3 side of the valve body 1, and a valve body 4, which closes the gas passing hole 5b when a seal surface 4c is stuck on a valve seat 2 and opens the gas passing hole 5b when the seal surface 4c separates from the valve seat 2 and which is formed of an engineering plastic of 1.1 to 1.2 specific gravity, is guided in a freely slidable manner by the valve body guide tube 5.