An automotive alternator (1) has slip-rings (37, 38) connected to a rotor shaft (33) and a brush device (5) covering the slip-rings. The brush device is composed of a brush holder (150) supporting brushes (51, 52) therein and a slip-ring cover (250) firmly connected to the brush holder. The slip-ring cover includes a wall (252) curved in a U-shape and a pair of flat walls (254, 256) closing the axial ends of the curved wall. Openings (C1) for ventilating the brushes and the slip-rings are formed between the curved wall (252) of the slip-ring cover and the sidewalls (155, 156) of the brush holder. When the brushes are positioned downward of the slip-rings, the openings (C1) are open to the downward of the slip-rings. Therefore, water is prevented from entering into the brush device (5) through the openings.