A method of controlling a refrigerator, the method comprising: when the refrigerator is turned on, performing a preliminary operation for constant temperature control; during the preliminary operation, determining by a controller whether a constant temperature control start condition is satisfied; when the constant temperature control start condition is satisfied, operating a cool air supply means (13, 21, 25) with a predetermined output; while the cool air supply means (13, 21, 25) operates with the predetermined output, determining, by the controller, an output of the cool air supply means (13, 21, 25) based on a current temperature of a storage compartment sensed by a temperature sensor (41, 42); and operating, by the controller, the cool air supply means (13, 21, 25) with the determined output, wherein the controller determines that the output of the cool air supply means (13, 21, 25) is decreased or increased when an absolute value of a difference between a previous temperature and a current temperature of the storage compartment is equal to or greater than a first reference value, and wherein the output of the cool air supply means (13, 21, 25) is decreased or increased again when the absolute value of the difference between a current temperature of the storage compartment sensed again after a predetermined time has elapsed and the previous temperature of the storage compartment is equal to or greater than the first reference value; characterized in that the controller - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the first reference value and is less than a second reference value greater than the first reference value, and - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a second level greater than the first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the second reference value. when the refrigerator is turned on, performing a preliminary operation for constant temperature control; during the preliminary operation, determining by a controller whether a constant temperature control start condition is satisfied; when the constant temperature control start condition is satisfied, operating a cool air supply means (13, 21, 25) with a predetermined output; while the cool air supply means (13, 21, 25) operates with the predetermined output, determining, by the controller, an output of the cool air supply means (13, 21, 25) based on a current temperature of a storage compartment sensed by a temperature sensor (41, 42); and operating, by the controller, the cool air supply means (13, 21, 25) with the determined output, wherein the controller determines that the output of the cool air supply means (13, 21, 25) is decreased or increased when an absolute value of a difference between a previous temperature and a current temperature of the storage compartment is equal to or greater than a first reference value, and wherein the output of the cool air supply means (13, 21, 25) is decreased or increased again when the absolute value of the difference between a current temperature of the storage compartment sensed again after a predetermined time has elapsed and the previous temperature of the storage compartment is equal to or greater than the first reference value; characterized in that the controller - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the first reference value and is less than a second reference value greater than the first reference value, and - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a second level greater than the first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the second reference value. - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the first reference value and is less than a second reference value greater than the first reference value, and - determines that the output of the cool air supply means (13, 21, 25) is decreased or increased by a second level greater than the first level when the absolute value of the difference between the previous temperature and the current temperature of the storage compartment is equal to or greater than the second reference value.