To prevent the leaked electromagnetic waves from containing any information and to eliminate the leakage of information by preparing a cover made of an electromagnetic wave shielding material which is opened when a file medium is loaded and unloaded and setting a personal computer device in a sleep state when an open state of the cover is detected.

When a medium inserting slot cover 3 is opened for the loading/ unloading of a file medium 4, a microswitch 5 is turned off. A sleep circuit 13 detects the OFF state of the switch 5 and sets a file control part 10, a display control part 11 and a main control part 12 in a sleep state respectively. Every part of the part 6 is kept in a sleep state and inactive while the cover 3 is kept open when the medium 4 is loaded an unloaded. Therefore, the medium inserting slot of a file device 2 has an opening part and no information is contained in the electromagnetic waves if leaked out. Thus, the leakage of information can be prevented.