PURPOSE: To enhance dehumidifying effect while suppressing the lowering of the strength of a housing to the min. by making it possible to enlarge the area of a cylindrical humidity control element by arranging the humidity control element to the housing so as to pierce the housing from one surface thereof to the other surface thereof.

CONSTITUTION: Holes 8, 9 are provided to the upper and lower surfaces of a housing 1 receiving a magnetic disk at the same position and a cylindrical humidity control element 10 is constructed between the holes 8, 9 to be connected to a DC power supply 6. Since the humidity control element 10 becoming the boundary of the air 2 in a housing and the open air 7 is formed into a cylindrical shape to increase the area thereof, the reduction effect of humidity in the housing is increased and the generation of dew condensation in the housing with the sudden change of the open air can be suppressed.