A gas production system which is configured to apply plasma to a catalyst in a reactor and reform a supplied source gas and a supplied oxidant gas to produce a product gas , the gas production system comprising: - source gas supply means for supplying the source gas to the reactor ; - oxidant gas supply means for supplying the oxidant gas to the reactor ; - gas ratio change means for changing a ratio between a supply amount of the source gas to be supplied to the reactor by the source gas supply means and a supply amount of the oxidant gas to be supplied to the reactor by the oxidant gas supply means , to make a state in which the oxidant gas is abundant as compared to the source gas ; and plasma generation means for generating the plasma to be applied to the catalyst, the gas production system further comprising: - a gas production device having the reactor , a first electrode and a second electrode for generating the plasma therebetween, and a catalyst layer provided in the reactor and containing the catalyst; and - an external power supply which is connected to the first electrode and the second electrode and generates voltage , wherein the plasma is generated in the reactor by the voltage generated by the external power supply and applied between the first electrode and the second electrode , wherein the catalyst layer is provided in the space between the first electrode and the second electrode . the gas production system comprising: - source gas supply means for supplying the source gas to the reactor ; - oxidant gas supply means for supplying the oxidant gas to the reactor ; - gas ratio change means for changing a ratio between a supply amount of the source gas to be supplied to the reactor by the source gas supply means and a supply amount of the oxidant gas to be supplied to the reactor by the oxidant gas supply means , to make a state in which the oxidant gas is abundant as compared to the source gas ; and plasma generation means for generating the plasma to be applied to the catalyst, - source gas supply means for supplying the source gas to the reactor ; - oxidant gas supply means for supplying the oxidant gas to the reactor ; - gas ratio change means for changing a ratio between a supply amount of the source gas to be supplied to the reactor by the source gas supply means and a supply amount of the oxidant gas to be supplied to the reactor by the oxidant gas supply means , to make a state in which the oxidant gas is abundant as compared to the source gas ; and plasma generation means for generating the plasma to be applied to the catalyst, the gas production system further comprising: - a gas production device having the reactor , a first electrode and a second electrode for generating the plasma therebetween, and a catalyst layer provided in the reactor and containing the catalyst; and - an external power supply which is connected to the first electrode and the second electrode and generates voltage , - a gas production device having the reactor , a first electrode and a second electrode for generating the plasma therebetween, and a catalyst layer provided in the reactor and containing the catalyst; and - an external power supply which is connected to the first electrode and the second electrode and generates voltage , wherein the plasma is generated in the reactor by the voltage generated by the external power supply and applied between the first electrode and the second electrode , wherein the catalyst layer is provided in the space between the first electrode and the second electrode . <EOS>