PURPOSE: To make a substantial reduction of a thermal load of an air cooling device and reduce a consumption power by a method wherein the number of operating air blowers for forcedly circulating cold air is reduced or their operating speed is reduced after an internal temperature of a storing chamber reaches a predetermined range of temperature.

CONSTITUTION: A partition wall 5 is arranged between an inlet port and an outlet port of an air cooling device 3 fixed to an upper part of a storing chamber 2 for use in storing item to be freezed. Both sides of the partition wall 5 form air passages communicating with both sides of the storing chamber 2. A plurality of air blowers 6 for use in forcedly circulating cold air are arranged in side-by-side relation in the midway of one air passage. Operating condition of these air blowers 6 is adjusted to reduce heat generated by the air blowers 6 in such a way as the number of operating air blower is reduced or the operating speed is reduced after an internal temperature in the storing chamber 2 reaches a predetermined temperature range. With this arrangement, it is possible to make a substantial reduction of a thermal load of the air cooling device and further to reduce a consumption power.