In an image forming device having a plurality of functions, a power measuring unit measures a power consumption of the image forming device, a power consumption computing unit computes a power consumption for execution of one of the plurality of functions based on the measured power consumption, a storage unit stores a target power consumption range for each of the plurality of functions, a measuring mode selecting unit selects one of a measuring mode and a non-measurement mode, and a power consumption estimation unit generates an estimated power consumption for execution of one of the plurality of functions in the non-measurement mode. The measuring mode selecting unit selects the measuring mode when the estimated power consumption in the non-measurement mode is beyond a target power consumption range for a corresponding function from the storage unit.