An ink jet printer includes: an image forming section (2) for forming an image by ejecting a pigment ink toward a recording medium in which a surficial layer includes thermoplastic fine particles, in a case (1); a fixing member (3) for fixing the image by heating and pressurizing the recording medium on which the image is formed by the image forming section; a combination deciding section (422a) for deciding a combination of a plurality of inks used for forming the image by the image forming section; a temperature detecting member (12) for detecting a temperature in the case (1); a humidity detecting member (13) for detecting a humidity in the case (1); and an ink volume adjusting section (422a) for adjusting volume of the inks ejected to a predetermined unit area of the recording medium when the image is formed by the image forming section, by changing the combination of the plurality of inks, which is decided by the combination deciding section, in accordance with the temperature detected by the temperature detecting member and the humidity detected by the humidity detecting member so that the volume of the inks is less than a first predetermined value.