According to an embodiment, a method for color erasing process includes the steps of: supplying a power to a heat source configured to heat a sheet having an image formed thereon using a color erasable material so as to cause heat generation as warming-up control; stopping the power supply to the heat source for a predetermined period of time in the warming-up control if the temperature of the heat source is increased starting from a temperature lower than a predetermined reference value that is lower than a color erasing temperature of the color erasable material and exceeds the predetermined reference value; performing maintenance control that is power supply control to maintain the temperature of the heat source at the target temperature; and performing, after the passage of the predetermined period of time, a color erasing process by the heat source.