A power management system comprising: a plurality of electric devices, each including a storage device adapted to store, for each of a plurality of operation levels, a corresponding operation algorithm information and power information, including a maximum instantaneous power, average power consumption and an operation time during which power is consumed, for each operation algorithm; and a power management unit adapted to receive power rate information from a power provider and the power information from each of the electric devices, and wherein the power management unit is adapted to determine a group of each of the electric devices to be one of a first group in which establishing an operation time of each electric device is possible, by determining that the operation time is assigned to the power information for each operation level of the electric device, a second group in which establishing the operation time of each electric device is not possible, by determining that the operation time is not assigned to power information for each operation level of the electric device, and otherwise a third group in which establishing the operation time and the operation level of each electric device is not possible, and, on the basis of the received power rate information and the power information of each device, to determine one of the operation levels for each electric device of the first and second group and transmit the determined operation level to the electric device, and to determine a recommended operation time and inform an user of the recommended operation time for each electric device of the third group, wherein each electric device comprises a controller adapted to control the electric device using the operation algorithm corresponding to the determined operation level transmitted from the power management unit or to a command from the user. a plurality of electric devices, each including a storage device adapted to store, for each of a plurality of operation levels, a corresponding operation algorithm information and power information, including a maximum instantaneous power, average power consumption and an operation time during which power is consumed, for each operation algorithm; and a power management unit adapted to receive power rate information from a power provider and the power information from each of the electric devices, and wherein the power management unit is adapted to determine a group of each of the electric devices to be one of a first group in which establishing an operation time of each electric device is possible, by determining that the operation time is assigned to the power information for each operation level of the electric device, a second group in which establishing the operation time of each electric device is not possible, by determining that the operation time is not assigned to power information for each operation level of the electric device, and otherwise a third group in which establishing the operation time and the operation level of each electric device is not possible, and, on the basis of the received power rate information and the power information of each device, to determine one of the operation levels for each electric device of the first and second group and transmit the determined operation level to the electric device, and to determine a recommended operation time and inform an user of the recommended operation time for each electric device of the third group, wherein each electric device comprises a controller adapted to control the electric device using the operation algorithm corresponding to the determined operation level transmitted from the power management unit or to a command from the user.