Abstract: An apparatus for supplying gas includes: an ion chamber; and a gas supply unit connected to the ion chamber, wherein the gas supply unit includes: a case having an internal space; an inactive gas supply unit connected to the ion chamber; and a hydrogen gas supply unit installed inside or outside of the case, wherein the hydrogen gas supply unit includes: a hydrogen gas generator generating hydrogen gas; a controller connected to the hydrogen gas generator; a dehumidifying filter connected to the controller and removing moisture from the hydrogen gas; and a purifying filter connected to the dehumidifying filter and removing an impurity from the hydrogen gas, wherein the hydrogen gas generator is configured to generate the hydrogen gas through a chemical reaction between a reactant and a hydrogen-containing solid raw material.