A cooling controlling apparatus for cooling an electronic apparatus, comprising: a cooling fan (54a-1, 54a-2; 54b-1, 54b-2) for discharging air in an inside of the electronic apparatus (50a; 50b) to an outside of the electronic apparatus (50a; 50b); an intake air temperature detector (13; 23) for detecting a temperature of air taken into the electronic apparatus (50a; 50b) by the cooling fan (54a-1, 54a-2; 54b-1, 54b-2); part temperature detectors (12a to 12c; 22a to 22c) for respectively detecting temperatures of each of a plurality of electronic parts (11a to 11c; 21a to 21c) arranged inside the electronic apparatus (50a; 50b); and a fan controller (15b; 25b, 25c) for controlling a rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) based on the temperature detected by the intake air temperature detector and the temperatures detected by the part temperature detectors when the fan controller is in a first mode, and for performing one of increasing and decreasing the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) using a predetermined variation ratio based on the temperatures detected by the part temperature detectors when all of the temperatures of the plurality of electronic parts are equal to or smaller than respective first threshold values provided for each of the electronic parts (11a to 11c; 21a to 21c) and the fan controller is in a second mode, wherein the fan controller (15b; 25b, 25c) is further configured to calculate a minimum rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) based on the detected intake air temperature, decrease the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) by the first variation ratio when the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) obtained by decreasing by the first variation ratio is equal to or larger than the minimum rotation number, and control the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) to be the minimum rotation number when the rotation number obtained by decreasing by the first variation ratio is smaller than the minimum rotation number. a cooling fan (54a-1, 54a-2; 54b-1, 54b-2) for discharging air in an inside of the electronic apparatus (50a; 50b) to an outside of the electronic apparatus (50a; 50b); an intake air temperature detector (13; 23) for detecting a temperature of air taken into the electronic apparatus (50a; 50b) by the cooling fan (54a-1, 54a-2; 54b-1, 54b-2); part temperature detectors (12a to 12c; 22a to 22c) for respectively detecting temperatures of each of a plurality of electronic parts (11a to 11c; 21a to 21c) arranged inside the electronic apparatus (50a; 50b); and a fan controller (15b; 25b, 25c) for controlling a rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) based on the temperature detected by the intake air temperature detector and the temperatures detected by the part temperature detectors when the fan controller is in a first mode, and for performing one of increasing and decreasing the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) using a predetermined variation ratio based on the temperatures detected by the part temperature detectors when all of the temperatures of the plurality of electronic parts are equal to or smaller than respective first threshold values provided for each of the electronic parts (11a to 11c; 21a to 21c) and the fan controller is in a second mode, wherein the fan controller (15b; 25b, 25c) is further configured to calculate a minimum rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) based on the detected intake air temperature, decrease the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) by the first variation ratio when the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) obtained by decreasing by the first variation ratio is equal to or larger than the minimum rotation number, and control the rotation number of the cooling fan (54a-1, 54a-2; 54b-1, 54b-2) to be the minimum rotation number when the rotation number obtained by decreasing by the first variation ratio is smaller than the minimum rotation number.