An object of this invention is to provide a responsive material gas concentration control system that can be mounted on a bubbling system and that can control a concentration of a material gas in a mixed gas at a constant value even though a partial pressure of the material gas fluctuates. The material gas concentration control system is used for a material evaporation system, and comprises a body that is connected to an outlet line and that has an internal flow channel for flowing the mixed gas, a concentration measuring part that measures the concentration of the material gas in the mixed gas, and a first valve that is arranged downstream of the concentration measuring part and that adjusts the measured concentration measured by the concentration measuring part at a previously determined set concentration, wherein the concentration measuring part and the first valve are mounted on the body.