An electric power demand regulating system which is adapted to regulate load applied to equipment of a power system by load apparatuses operated by electric power from the power system which supplies electric power to consumers, comprises an electric power demand regulating device adapted to: make selection of a load apparatus to be requested to make a change of an operation state on basis of a regulation target value, which is an amount of load to be regulated, and a load information for each apparatus, which is information of each load apparatus when the load on the equipment is regulated, and outputting of a change request for requesting to make a change of the operation state of the selected load apparatus plural times during a period from start to completion of regulation;. update the regulation target value after the change request is outputted and select the load apparatus to be requested to make a change of the operation state at a next change request on basis of the updated regulation target value; select the load apparatus to be requested to make a change of the operation state on basis of the regulation target value, the load information for each apparatus and further more a degree of change in convenience of the consumers in case where the operation state of the load apparatuses is changed; and maintain a response rate representing a probability that the operation state is changed when the change request is received for each category of the load apparatuses, update the response rate when the change request is received according to the category of the load apparatus and select the load apparatus to be requested to make a change of the operation state on basis of the regulation target value, the load information for each apparatus and further more the response rate. make selection of a load apparatus to be requested to make a change of an operation state on basis of a regulation target value, which is an amount of load to be regulated, and a load information for each apparatus, which is information of each load apparatus when the load on the equipment is regulated, and outputting of a change request for requesting to make a change of the operation state of the selected load apparatus plural times during a period from start to completion of regulation;. update the regulation target value after the change request is outputted and select the load apparatus to be requested to make a change of the operation state at a next change request on basis of the updated regulation target value; select the load apparatus to be requested to make a change of the operation state on basis of the regulation target value, the load information for each apparatus and further more a degree of change in convenience of the consumers in case where the operation state of the load apparatuses is changed; and maintain a response rate representing a probability that the operation state is changed when the change request is received for each category of the load apparatuses, update the response rate when the change request is received according to the category of the load apparatus and select the load apparatus to be requested to make a change of the operation state on basis of the regulation target value, the load information for each apparatus and further more the response rate.