Erasing device, image forming apparatus, and erasing method

An erasing device includes a line scanner on an upstream side in a recording medium conveying direction, includes a thermal head downstream in the recording medium conveying direction of the line scanner, and includes a platen in a position opposed to the thermal head as a heating device across a recording medium conveying path. The erasing device causes the heat generating elements of the thermal head in positions corresponding to color and density sensors in positions of an image detected by the line scanner to generate heat. The erasing device controls, according to detected colors or density, a quantity of heat to be generated.