Abstract: A magnetic disk apparatus includes a housing having a sealed spaced between a base and a cover plate. An electric motor is situated within the housing. The electric motor includes a shaft extending between the base and the cover plate, a rotor situated coaxially around the shaft, and a rolling bearing situated between the rotor and the shaft. A magnetic recording medium is supported on the rotor. The rotor has a seal portion interposed between the cover plate and the rolling bearing. The seal portion includes a first surface located near the outer peripheral surface of the shaft and defining a first gap between the first surface itself and the outer peripheral surface of the shaft and a second surface located near the cover plate and defining a second gap between the second surface itself and the cover plate. The first and second gaps communicate with each other to form a labyrinth seal between the space and the rolling bearing.