A system comprising: an engine, an automatic transmission connected to the engine and having a manual mode manually select a desired gear ratio from a plurality of fixed gear ratios, and a control device comprising a manual mode detection unit configured to detect whether the automatic transmission is set in the manual mode, characterized in that the engine comprises a supercharger configured to compress an intake air of the engine, and the control device further comprises: a temperature sensor as a temperature detection unit configured to detect a temperature of the supercharger; a temperature judgment unit configured to judge whether the temperature of the supercharger detected by the temperature detection unit is higher than or equal to a predetermined value; and a gear ratio changeover unit (43, 45) configured to change the gear ratio of the automatic transmission to a higher one of the fixed gear ratios such that a rotation speed of the engine is lowered by shifting to the higher gear ratio when the manual mode detection unit detects that the automatic transmission is set in the manual mode and when the temperature judgment unit judges that the temperature of the supercharger is higher than or equal to the predetermined value. an engine, an automatic transmission connected to the engine and having a manual mode manually select a desired gear ratio from a plurality of fixed gear ratios, and a control device comprising a manual mode detection unit configured to detect whether the automatic transmission is set in the manual mode, characterized in that the engine comprises a supercharger configured to compress an intake air of the engine, and the control device further comprises: a temperature sensor as a temperature detection unit configured to detect a temperature of the supercharger; a temperature judgment unit configured to judge whether the temperature of the supercharger detected by the temperature detection unit is higher than or equal to a predetermined value; and a gear ratio changeover unit (43, 45) configured to change the gear ratio of the automatic transmission to a higher one of the fixed gear ratios such that a rotation speed of the engine is lowered by shifting to the higher gear ratio when the manual mode detection unit detects that the automatic transmission is set in the manual mode and when the temperature judgment unit judges that the temperature of the supercharger is higher than or equal to the predetermined value. a temperature sensor as a temperature detection unit configured to detect a temperature of the supercharger; a temperature judgment unit configured to judge whether the temperature of the supercharger detected by the temperature detection unit is higher than or equal to a predetermined value; and a gear ratio changeover unit (43, 45) configured to change the gear ratio of the automatic transmission to a higher one of the fixed gear ratios such that a rotation speed of the engine is lowered by shifting to the higher gear ratio when the manual mode detection unit detects that the automatic transmission is set in the manual mode and when the temperature judgment unit judges that the temperature of the supercharger is higher than or equal to the predetermined value.