To provide a supercharger system of an internal combustion engine, which both reduces heat capacity of a turbine housing and improves turbo efficiency, at the same time.

The heat capacity of the turbine housing 2 is reduced by adopting an aluminum alloy as a constituting material of the turbine housing 2. The turbine housing 2 is cooled by engine cooling water so that the ratio of the temperature of the turbine housing 2 and the temperature of a turbine wheel 51, becomes the relationship of the reciprocal ratio, to the ratio of an expansion coefficient of the constituting material of the turbine housing 2 and an expansion coefficient of a constituting material of the turbine wheel 51. Thus, both early activation of a catalyst by reduction in the heat capacity of the turbine housing 2 and continuous security of high turbo efficiency by maintenance of a tip clearance, are made compatible.