A system for controlling multiple air conditioners including a plurality of indoor units, the system being characterized by comprising: a demand control unit (120, 220, 320) configured to divide the multiple air conditioners into groups, to assign a priority level to each group, to calculate an estimated power amount used by the multiple air conditioners based on an amount of power consumed by the multiple air conditioners during a predetermined time period, and to forcibly control an operation of one or more air conditioners included in a respective group based on the priority level assigned to the respective group, wherein the demand control unit (120, 220, 320) comprises: an operation rate calculating unit (124, 221, 324) configured to compare the estimated power amount and a pre-set target power amount, and to calculate an operation rate of the multiple air conditioners based on a result of the comparison; a priority level determining unit (122, 222, 322) configured to divide the multiple air conditioners into the groups, and to assign the priority level to each group; a control unit (123, 223, 323) configured to forcibly control the operation of the one or more multiple air conditioners included in the respective group based on the priority level assigned to the respective group; and a high priority level setting unit (125, 224, 325) configured to set at least one air conditioner to have a highest priority level so as to exclude the at least one air conditioner having the highest priority level from being forcibly controlled, and wherein the groups are automatically determined by the control unit based upon previous operation characteristics of the air conditioners, temperature differences in the rooms of the building, and pre-assigned values given to the air conditioners. a demand control unit (120, 220, 320) configured to divide the multiple air conditioners into groups, to assign a priority level to each group, to calculate an estimated power amount used by the multiple air conditioners based on an amount of power consumed by the multiple air conditioners during a predetermined time period, and to forcibly control an operation of one or more air conditioners included in a respective group based on the priority level assigned to the respective group, wherein the demand control unit (120, 220, 320) comprises: an operation rate calculating unit (124, 221, 324) configured to compare the estimated power amount and a pre-set target power amount, and to calculate an operation rate of the multiple air conditioners based on a result of the comparison; a priority level determining unit (122, 222, 322) configured to divide the multiple air conditioners into the groups, and to assign the priority level to each group; a control unit (123, 223, 323) configured to forcibly control the operation of the one or more multiple air conditioners included in the respective group based on the priority level assigned to the respective group; and a high priority level setting unit (125, 224, 325) configured to set at least one air conditioner to have a highest priority level so as to exclude the at least one air conditioner having the highest priority level from being forcibly controlled, and wherein the groups are automatically determined by the control unit based upon previous operation characteristics of the air conditioners, temperature differences in the rooms of the building, and pre-assigned values given to the air conditioners. an operation rate calculating unit (124, 221, 324) configured to compare the estimated power amount and a pre-set target power amount, and to calculate an operation rate of the multiple air conditioners based on a result of the comparison; a priority level determining unit (122, 222, 322) configured to divide the multiple air conditioners into the groups, and to assign the priority level to each group; a control unit (123, 223, 323) configured to forcibly control the operation of the one or more multiple air conditioners included in the respective group based on the priority level assigned to the respective group; and a high priority level setting unit (125, 224, 325) configured to set at least one air conditioner to have a highest priority level so as to exclude the at least one air conditioner having the highest priority level from being forcibly controlled, and wherein the groups are automatically determined by the control unit based upon previous operation characteristics of the air conditioners, temperature differences in the rooms of the building, and pre-assigned values given to the air conditioners.