The invention relates to the construction of an in-vehicle magnetic disk drive and a case for holding the in-vehicle magnetic disk drive. The in-vehicle magnetic disk drive must meet a condition peculiar thereto requiring normal operations under severe temperature conditions. An environment of an excessively low temperature disturbs a normal information recording operation, while an environment of an excessively high temperature makes the retention of recorded information impossible. The case is provided with a cold insulator, a heat insulator, a heat insulating material and a temperature sensor and is set in a specific position. The operation of the magnetic disk drive at temperatures outside a predetermined temperature range is inhibited.