To provide an ink jet recorder which exerts a high diagnosing capability when simple X-ray images for medical use are recorded.

In the ink jet recorder 100 for recording medical use images onto recording media with the use of a plurality of black inks having different concentrations, images are recorded by the control of a control means 101, so that a granularity of recording images at a density region of a transmission/ diffusion density of 2.0-2.5 is superior to a granularity of recording images at a density region of the transmission/diffusion density of 1.0-2.0.