A cooling system including an evaporator to exchange heat with air, a frost detector installed on the evaporator to detect frost, and a control unit to determine whether a current time corresponds to a frost detection point, to control the frost detector to operate when the current time corresponds to the frost detection point, and to control a defrosting operation based on a frost detection signal from the frost detector. It is possible to accurately detect the amount of frost formed on the evaporator by executing the frost detection under constant frost detection environmental conditions.