PURPOSE: To improve the illumination effect during warm storage and prevent erroneous use by the user.

CONSTITUTION: A cool temperature-switching chamber 7 is provided at a part of a chamber 4 designed to be cooled to a low temperature. An electric heater 13 is provided as a means of heating to change the cool temperature-switching chamber 7 to a chamber conditioned to a state for the warm storage. An illumination lamp 2 and a heater switch, the former for illuminating the cool temperature-switching chamber 7 with a warm shade of light and the latter for controlling the application of power to the electric heater 13, are provided in a setup to effect the lighting of the illumination lamp 2 by switching interlocking with the application of power by the heater switch to the electric heater 13.