A one-way valve device or a non-return valve mechanism in the valve device provides a higher retaining residual pressure without upsizing. A non-return valve cassette in a consumption valve device regulates gas flow. The cassette includes a check valve movable forward and backward between a valve-closed position and a valve-open position in an outlet secondary flow channel and movable backward to the valve-open position under pressure of the gas flowing upstream, and a first coil spring with a spring force biasing the check valve upstream. The first coil spring permits the check valve to move downstream against the upstream biasing when an upstream pressure is a predetermined pressure or greater. The check valve includes a downstream end smaller than an upstream end in an area communicating with an upstream space at the valve-closed position.