To provide an ink conditioning method by which the state of ink (ink concentration, for example) formed at an image carrier and the like is detected and the material value of the ink (surface tension of the ink, for example) is changed based on the detected result and an image forming device using this method.

This image forming device 1 is constituted so that a 1st latent image corresponding to image information is formed on the image carrier 6 and an ink image is formed by supplying the ink 11 to the carrier 6 from a developing device 12 and developing the latent image. Besides, the ink image is transferred on a sheet 14. Then, a 2nd latent image is formed on the carrier 6 and the ink image is formed by supplying the ink 11 to the carrier 6 from the developing device 12. Besides, the density of the ink image is measured by a photosensor 32. Based on the measured value, the prescribed quantity of conditioner for adjusting the material value of the ink is supplied to the ink container 24 of the developing device 12 from a tank 35.