A process apparatus includes a gas supplier which supplies a reaction gas having a constant concentration, and a processor which performs a predetermined process by the reaction gas supplied from the gas supplier, where the gas supplier includes a reactor which accommodates a solid phase reactant, a heater which applies heat to the solid phase reactant to convert the solid phase reactant to a reaction gas in a gas phase, a gas pump which applies a predetermined pumping pressure to the reactor, and a gas outlet which discharges the reaction gas to the processor.