A filtering device for the air taken in by an internal combustion engine; the filtering device comprising: an air-box, which defines inside it a cavity and has at least an inlet opening toward the outside and at least an outlet opening toward an engine intake system; at least a filter, which is housed inside the air-box and is arranged between the inlet opening and the outlet opening; a drainage through-hole, which is obtained through a lower wall of the air-box and is designed to allow the drainage of any residual water inside the air-box; and a valve, usually closed, which is coupled to the drainage hole; the filtering device being characterized in that: the valve comprises: a mechanical shutter which is movable between a closed position, where it closes the drainage hole, and an open position, where it lets the drainage hole free to allow the drainage of any residual water inside the air-box; an elastic element that pushes the shutter toward the closed position; and an actuator which is operable to move the shutter from the closed position to the open position against the elastic force generated by the spring; and a control unit that controls the actuator, the control unit is connectable to a rain sensor or to a control device of a windshield wiper, and sets the valve opening depending on the fact that the rain sensor detects the presence of rain or on the fact that the control device of the windshield wiper is activated. an air-box, which defines inside it a cavity and has at least an inlet opening toward the outside and at least an outlet opening toward an engine intake system; at least a filter, which is housed inside the air-box and is arranged between the inlet opening and the outlet opening; a drainage through-hole, which is obtained through a lower wall of the air-box and is designed to allow the drainage of any residual water inside the air-box; and a valve, usually closed, which is coupled to the drainage hole; the filtering device being characterized in that: the valve comprises: a mechanical shutter which is movable between a closed position, where it closes the drainage hole, and an open position, where it lets the drainage hole free to allow the drainage of any residual water inside the air-box; an elastic element that pushes the shutter toward the closed position; and an actuator which is operable to move the shutter from the closed position to the open position against the elastic force generated by the spring; and a control unit that controls the actuator, the control unit is connectable to a rain sensor or to a control device of a windshield wiper, and sets the valve opening depending on the fact that the rain sensor detects the presence of rain or on the fact that the control device of the windshield wiper is activated. the valve comprises: a mechanical shutter which is movable between a closed position, where it closes the drainage hole, and an open position, where it lets the drainage hole free to allow the drainage of any residual water inside the air-box; an elastic element that pushes the shutter toward the closed position; and an actuator which is operable to move the shutter from the closed position to the open position against the elastic force generated by the spring; and a control unit that controls the actuator, the control unit is connectable to a rain sensor or to a control device of a windshield wiper, and sets the valve opening depending on the fact that the rain sensor detects the presence of rain or on the fact that the control device of the windshield wiper is activated.