A supercharging device for an engine is provided, which includes a supercharger provided to an intake passage of the engine, an actuator configured to drive the supercharger, and a controller including a processor configured to control the actuator to drive the supercharger when an operating state of the engine is in a given supercharging range, and to stop the supercharger when the operating state is in a non-supercharging range. The controller estimates an amount of condensate accumulated in an oil pan, and the controller causes the actuator to forcibly drive the supercharger when the estimated amount of condensate is more than a preset amount, even if the operating state is in the non-supercharging range.