PURPOSE: To prevent the lowering of the reliability of the record information in case a magnetic disk device is started at an abnormal temperature, by detecting the temperature of the air taken inside from outside and inhibiting the use of the disk device at the abnormal temperature.

CONSTITUTION: When a disk device starts its operation, a disk medium within an HDA4 starts its rotation. Then a control circuit 9 performs the initialization for the HDA4 and the circuit 9 itself. The information showing that a disk device is applicable is given to an upper device via an interface cable 11 unless no abnormal signal is fed to the circuit 9 from a temperature detector 7. On the other hand, the signal showing the abnormal temperature of the inhaled air is fed to the circuit 9 from the detector 7. In such case, the circuit 9 feeds no signal showing the READY state to the upper device. Thus the upper device is impossible to use the disk device.