PURPOSE: To maintain proper humidity inside by supplying electric power to a humidification heater when humidification is required and to a compressor when dehumidification is required based on a detection output of a temperature sensor and opening a motor-driven damper and closing the motor-driven damper except for dehumidification time.

CONSTITUTION: A temperature control device 13 is designed to detect temperature by way of a temperature sensor 12 and supply electric power to a heater 9 when heating is required and to a compressor 3 when cooling is required. It detects humidity by way of a humidity sensor 39 and supplies electric power to a humidification heater 30 when humidification is required and to the compressor 3 when dehumidification is required, simultaneously opening motor-driven dampers 34 and 35 for action. When the dampers 34 and 35 are opened, a housing box 20 communicates with the space between the box 20 and a casing 1, which allows the air in the refrigerator to pass through the spaces and start circulation when the air enters the refrigerator again. Therefore, the water content in the air in the refrigerator is dehumidified by a vaporizer 6. The motor-driven dampers are closed except when dehumidification is required.