An on-demand power control system in which dynamic priority control is performed, comprising: a power source; a plurality of electrical devices; a home appliance agent that controls supply of power to each electrical device by receiving a signal having a power value from a smart tap or each electrical device, by calculating requested power and a priority on the basis of the received signal, by transmitting the requested power and the priority as a power request message to a power manager, and by transmitting a function control command for controlling the electrical device to the electrical device according to a power assignment message received from the power manager; the power manager that obtains power to be assigned to each electrical device according to the priorities between the electrical devices on the basis of the power request message from each electrical device received from the home appliance agent; and a home appliance DB connected to the power manager and/or the home appliance agent, the home appliance agent, the power manager and the home appliance DB constituting a network connected to the electrical devices through the smart taps, wherein the power manager determines power to be assigned to each electrical device by inquiring the home appliance agent of whether or not the electrical device is capable of adjusting an operating function mode set as a target of a service operation of the electrical device, and of power for the electrical device, wherein if the electrical device is capable of adjusting the operating function mode, the power manager obtains as a power assignment message the operating function mode set as a target for the electrical device and/or a power mode having necessary power and necessary time for reaching the operating function mode set as a target; wherein if the electrical device is not capable of adjusting the operating function mode, the power manager obtains a power mode as a power assignment message without considering the operating function mode, and wherein the power manager includes a memory for transmitting the power assignment message thus obtained to the home appliance agent, wherein the power manager is configured to control a power supply to the electrical devices such that an upper limit for integral power over a fixed period and a maximum instantaneous power is not exceeded, and wherein an instantaneous power is consumed power and the maximum instantaneous power is an upper limit for the instantaneous power. a power source; a plurality of electrical devices; a home appliance agent that controls supply of power to each electrical device by receiving a signal having a power value from a smart tap or each electrical device, by calculating requested power and a priority on the basis of the received signal, by transmitting the requested power and the priority as a power request message to a power manager, and by transmitting a function control command for controlling the electrical device to the electrical device according to a power assignment message received from the power manager; by receiving a signal having a power value from a smart tap or each electrical device, by calculating requested power and a priority on the basis of the received signal, by transmitting the requested power and the priority as a power request message to a power manager, and by transmitting a function control command for controlling the electrical device to the electrical device according to a power assignment message received from the power manager; the power manager that obtains power to be assigned to each electrical device according to the priorities between the electrical devices on the basis of the power request message from each electrical device received from the home appliance agent; and a home appliance DB connected to the power manager and/or the home appliance agent, the home appliance agent, the power manager and the home appliance DB constituting a network connected to the electrical devices through the smart taps, wherein the power manager determines power to be assigned to each electrical device by inquiring the home appliance agent of whether or not the electrical device is capable of adjusting an operating function mode set as a target of a service operation of the electrical device, and of power for the electrical device, wherein if the electrical device is capable of adjusting the operating function mode, the power manager obtains as a power assignment message the operating function mode set as a target for the electrical device and/or a power mode having necessary power and necessary time for reaching the operating function mode set as a target; wherein if the electrical device is not capable of adjusting the operating function mode, the power manager obtains a power mode as a power assignment message without considering the operating function mode, and wherein the power manager includes a memory for transmitting the power assignment message thus obtained to the home appliance agent, wherein the power manager is configured to control a power supply to the electrical devices such that an upper limit for integral power over a fixed period and a maximum instantaneous power is not exceeded, and wherein an instantaneous power is consumed power and the maximum instantaneous power is an upper limit for the instantaneous power.