An air-conditioner operation controlling device controls each individual air-conditioner in a server room wherein are disposed a plurality of server racks for containing servers and a plurality of air conditioners for cooling the server racks. The air-conditioner operation controlling device includes an air-conditioning load calculating portion calculating air-conditioning loads of zones handled by individual air-conditioners from electric current values of the individual server racks; and a controlling portion controlling each individual air-conditioner through outputting, to each individual air-conditioner, a return air temperature setting value, by calculating, for each individual air-conditioner, a return air temperature setting value so that the supply air temperature for each of the air-conditioners is no less than a specific value, based on the air-conditioning loads and on the maximum temperature differentials between the return air temperature and the supply air temperature for each individual air-conditioner.