To provide an image forming method for forming an image which has no image density variation even if using a recording medium having no ink receiving layer such as industrial printing paper, and also has high image density and no bleeding.

A preprocessing liquid S is discharged to a recording medium P from a preprocessing liquid applicator, as shown in Fig. (1), before an ink droplet I is discharged to the recording medium P from print heads 21 to 24. In this case, an amount of the preprocessing liquid S is made such that the liquid S completely penetrate into the recording medium P as shown in Fig. (2) before the ink droplet I lands on the recording medium P. By thus controlling the amount of the preprocessing liquid S, the preprocessing liquid S has completely penetrated into the recording medium when the ink droplet I lands on the recording medium P. As a result, a dot shape D ideal for forming an image is formed in the recording medium P as shown in Fig. (3), so that a high quality image is formed as shown in Fig. (4).