1. An internal combustion engine in which an amount of production of soot gradually increases and then peaks when an amount of recirculated exhaust gas supplied in a combustion chamber increases and in which a further increase of the amount of recirculated exhaust gas supplied in the combustion chamber results in a temperature of fuel and surrounding gas in the combustion chamber becoming lower than a temperature of production of soot and therefore almost no production of soot any longer, said engine comprising: switching means for selectively switching between a first combustion where the amount of the recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas where the amount of production of soot peaks and almost no soot is produced and a second combustion where the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated exhaust gas where the amount of production of soot peaks and exhaust gas recirculation rate control means for changing the exhaust gas recirculation rate in a step-like manner when switching from the first combustion to the second combustion or from the second combustion to the first combustion.