A sealing apparatus for sealing a magnetic disk drive. The sealing apparatus includes a base member on which heat generating parts are mounted, a sealing member provided on and adhering to a circumferential edge of the base member, and a lid member secured to the base member via the sealing member for covering an internal space enclosed with the base member and the lid member. The lid member has a downwardly extending peripheral portion which comes in contact with the sealing member, and is arranged on the sealing member such that the downwardly extending peripheral portion is placed substantially on a centerline of the sealing member lying in the middle of a width of the circumferential edge of the base member. The sealing apparatus of the present invention can prevent the sealing member from deviating or separating from an original position on the base member when the base member is subject to thermal expansion due to heat generated from the heat generating parts mounted on the base member, and it is possible to stably maintain a sealing condition of the magnetic disk drive over a long period of time of practical use.