A ventilation path is provided for communicating an accommodation chamber wherein a transmission mechanism for an electric motor is accommodated and an external space. A covering space is provided for covering an outer end opening of the ventilation path is opened to suppress formation of a water film at the outer end opening. A throttle apparatus includes a housing with covering walls defining covering spaces having open ports which are open to an external space. Lower end openings of ventilation paths are provided for communicating the external space and the accommodation chamber with each other are open to the covering spaces. The opening ports are set to such a size that adhering water flowing down along the lower outer face is cut into pieces between the covering walls and a housing body across the open ports.