PURPOSE: To effectively judge even if a condition of heavy cooling load exists at a defrosting interval to control defrosting with high reliability and to suppress temperature rise in a refrigerator by providing a controller for varying the interval by judging the magnitude of the load.

CONSTITUTION: A first timer 40 for integrating operating time of a compressor 26 is provided. Since frosting deposition of a cooler is increased with increased cooling load to increase chilled gas flowing resistance, chilled gas circulating amount in a refrigerator is reduced. As a result, a phenomenon in which the damper of a motor-driven damper in a cold storage chamber is 'opened' is utilized, it is defrosted by a second timer 42 for counting the number of times of continuous 'opening' states of the damper when a heavy condition of a cooling load (e.g., a door is forgotten to be closed, a door is frequently opened and closed) normally exists at an interval of defrosting by the timer 40 by a defrost controller 44 having the timer 42. Thus, defrost control with high reliability can be obtained.