A supercharging device for an engine, comprising: a supercharger to be provided to an intake passage of the engine; an actuator configured to drive the supercharger; a blowby gas introduction part from a blowby gas passage to the intake passage passage which is formed in an upper wall part upstream of the supercharger; and a controller configured to control the actuator to drive the supercharger when an operating state of the engine is in a given supercharging range, and control the actuator to stop or drive the supercharger when the operating state is in a non-supercharging range, wherein the controller is configured to estimate an amount of condensate in an oil pan, and the controller is configured to control the actuator to drive the supercharger when the estimated amount of condensate is equal to or more than a preset amount and the operating state is in the non-supercharging range, characterized in that the actuator includes an electromagnetic clutch configured to engage or release the supercharger with an output shaft of the engine, a bypass passage bypassing the supercharger, and a bypass valve disposed in the bypass passage, the controller is configured to determine whether a temperature of the supercharger is lower than a preset temperature in the non-supercharging range, the controller is configured to control the actuator to release the electromagnetic clutch and open the bypass valve, when the estimated amount of condensate is less than the preset amount and when the temperature of the supercharger is lower than the preset temperature, and the controller is configured to switch the electromagnetic clutch to an imperfectly-engaged state, close the bypass valve and determine whether a supercharger rotation speed is less than a preset rotation speed, when the estimated amount of condensate is equal to or more than the preset amount, and if the rotation speed of the supercharger is less than the preset rotation speed then the controller turns off the electromagnetic clutch, and if the rotation speed of the supercharger is equal to or more than the preset rotation speed then the controller switches the electromagnetic clutch to the engaged state. a supercharger to be provided to an intake passage of the engine; an actuator configured to drive the supercharger; a blowby gas introduction part from a blowby gas passage to the intake passage passage which is formed in an upper wall part upstream of the supercharger; and a controller configured to control the actuator to drive the supercharger when an operating state of the engine is in a given supercharging range, and control the actuator to stop or drive the supercharger when the operating state is in a non-supercharging range, wherein the controller is configured to estimate an amount of condensate in an oil pan, and the controller is configured to control the actuator to drive the supercharger when the estimated amount of condensate is equal to or more than a preset amount and the operating state is in the non-supercharging range, characterized in that the actuator includes an electromagnetic clutch configured to engage or release the supercharger with an output shaft of the engine, a bypass passage bypassing the supercharger, and a bypass valve disposed in the bypass passage, the controller is configured to determine whether a temperature of the supercharger is lower than a preset temperature in the non-supercharging range, the controller is configured to control the actuator to release the electromagnetic clutch and open the bypass valve, when the estimated amount of condensate is less than the preset amount and when the temperature of the supercharger is lower than the preset temperature, and the controller is configured to switch the electromagnetic clutch to an imperfectly-engaged state, close the bypass valve and determine whether a supercharger rotation speed is less than a preset rotation speed, when the estimated amount of condensate is equal to or more than the preset amount, and if the rotation speed of the supercharger is less than the preset rotation speed then the controller turns off the electromagnetic clutch, and if the rotation speed of the supercharger is equal to or more than the preset rotation speed then the controller switches the electromagnetic clutch to the engaged state.