A cooling tower controlling system for controlling a plurality of cooling towers (11,12,13) that perform temperature control of cooling water used for heat exchange with equipment, comprising: the plurality of cooling towers each having a cooling fan (11a,12a,13a), a rotation driving unit (M1,M2,M3) which is a driving source for rotating the cooling fan, a supplying unit (L31, 11b,11c,L32, 12b,12c,L33, 13b,13c) that supplies circulating cooling water that has passed through a heat exchange unit of the equipment to the cooling tower, and a storage unit that stores the circulating cooling water that has been cooled by air blowing of the cooling fan; a plurality of pumps (P1,P2,P3) that send the circulating cooling water from the storage unit to the heat exchange unit of the equipment; a circulation line having a pipe that connects respectively between the storage unit and the pumps, between the pumps and the heat exchange unit of the equipment, and between the heat exchange unit and the supplying units of the cooling towers, so as to allow the circulating cooling water to flow therethrough; a temperature measuring unit that measures a temperature of the circulating cooling water within the circulation line at a position upstream of the heat exchange unit and downstream of the storage unit or a temperature of the circulating cooling water within the storage unit or within the pumps; a first load controlling unit that controls a rotational speed of the cooling fans with respective rotation driving units so that an absolute value ΔTE of a difference between the temperature TE1 measured in the temperature measuring unit and an outside air wet-bulb temperature TE0 comes within a first approach temperature AP1, which corresponds to a first load, in a first load period of the equipment; and a second load controlling unit that controls the rotational speed of the cooling fans with respective rotation driving units so that the absolute value ΔTE of the difference between the temperature TE1 measured in the temperature measuring unit and the outside air wet-bulb temperature TE0 comes within a second approach temperature AP2, which corresponds to a second load higher than the first load and has a lower value than the first approach temperature AP1, in the second load period of the equipment. the plurality of cooling towers each having a cooling fan (11a,12a,13a), a rotation driving unit (M1,M2,M3) which is a driving source for rotating the cooling fan, a supplying unit (L31, 11b,11c,L32, 12b,12c,L33, 13b,13c) that supplies circulating cooling water that has passed through a heat exchange unit of the equipment to the cooling tower, and a storage unit that stores the circulating cooling water that has been cooled by air blowing of the cooling fan; a plurality of pumps (P1,P2,P3) that send the circulating cooling water from the storage unit to the heat exchange unit of the equipment; a circulation line having a pipe that connects respectively between the storage unit and the pumps, between the pumps and the heat exchange unit of the equipment, and between the heat exchange unit and the supplying units of the cooling towers, so as to allow the circulating cooling water to flow therethrough; a temperature measuring unit that measures a temperature of the circulating cooling water within the circulation line at a position upstream of the heat exchange unit and downstream of the storage unit or a temperature of the circulating cooling water within the storage unit or within the pumps; a first load controlling unit that controls a rotational speed of the cooling fans with respective rotation driving units so that an absolute value ΔTE of a difference between the temperature TE1 measured in the temperature measuring unit and an outside air wet-bulb temperature TE0 comes within a first approach temperature AP1, which corresponds to a first load, in a first load period of the equipment; and a second load controlling unit that controls the rotational speed of the cooling fans with respective rotation driving units so that the absolute value ΔTE of the difference between the temperature TE1 measured in the temperature measuring unit and the outside air wet-bulb temperature TE0 comes within a second approach temperature AP2, which corresponds to a second load higher than the first load and has a lower value than the first approach temperature AP1, in the second load period of the equipment.