During the catalyst warm-up period, when control enabling reduction in hydrocarbons is not executed in gasoline engine 100, the opening of the throttle valve 101 is made smaller in order to reduce the hydrocarbon discharge. During the catalyst warm-up period, when control enabling reduction in the quantity of hydrocarbons is executed in gasoline engine 100, the opening of the throttle valve 101 is made larger in order to accelerate warm-up of the catalyst, thereby shortening the catalyst warm-up period. A shorter catalyst warm-up period enables reduction in the total quantity of hydrocarbons from engine startup to the end of the catalyst warm-up period.