The present invention is one that prevents standard gas from remaining in a standard gas line to prevent a concentration of standard gas from being reduced due to adsorption, modification, or the like, and has: a diluent gas line provided with a diluent gas flow rate controlling mechanism; a standard gas line provided with a standard gas flow rate controlling mechanism; an output gas line joined by the diluent gas line and standard gas line and outputs the standard gas having a predetermined concentration; an exhaust gas line connected to an upstream side of the standard gas flow rate controlling mechanism in the standard gas line and provided with an on/off valve and a flow rate control part; and a control part that, depending on a flow rate of the standard gas flowing through the standard gas line or the type of the standard gas, switches on/off the on/off valve.