To provide an inexpensive check valve excellent in assembling workability and operation reliability, and a gas compressor using the valve.

A valve element 52 and a bush 54 are arranged in a vertical hole-like passage 51 connecting an intake chamber 11 and a backpressure chamber 23, as structure of the check valve. The valve element 52 is sucked up instantaneously from a valve seat part 53 of the bush 54 to be separated so as to open the passage 51 by a pressure difference when pressure of the chamber 23 gets lower than that of the intake chamber 11, and the valve element 52 falls down and contacts closely onto a valve seat 53 side by its dead weight to close the passage 51 when sucking-up force therein gets small.