A compressed natural gas charging system includes a gas charging passageway whose one end is capable of being connected to a compressed natural gas supply device capable of supplying a compressed natural gas and whose other end opens into a gas vessel, and a one-way valve incorporated in the gas charging passageway to permit the compressed natural gas to flow from the one end of the gas charging passage through the one-way valve toward the other end. In the compressed natural gas charging system, a constriction is provided in the gas charging passageway downstream of the one-way valve and has a constriction degree larger than that of the one-way valve. Thus, it is possible to prevent an excessive temperature drop due to the adiabatic expansion of the compressed natural gas from occurring across the one-way valve and to rapidly charge the compressed natural gas, and it is unnecessary to use an expensive material for a part of or constituting the one-way valve.