According to one embodiment, a printer includes a conveying mechanism, a first image forming unit, and a second image forming unit. The conveying mechanism conveys a medium. The first image forming unit forms an image with a non-temperature-sensitive ink whose color is not changed depending on a temperature, on the medium. The second image forming unit forms an image with a temperature-sensitive ink whose color is changed depending on a temperature, on the medium having the image with the non-temperature-sensitive ink formed thereon.