An internal combustion engine is provided with an EGR system (10) comprising, in an EGR passage (Eg), an EGR valve (12) and a reed valve (13), and is provided with a control device (20) that expresses the relation between the opening degree (xegr) of the EGR valve (12) and the mass flow rate (megr) of EGR gas using the first volume flow rate (V1) of the EGR gas, which is expressed using an equation for the isentropic flow of a nozzle of the EGR valve (12), and the second volume flow rate (V2) of the EGR gas pumped out by the reed valve (13), thereby being able to accurately calculate the mass flow rate of the EGR gas even if being provided with the reed valve (check valve) in the EGR passage.