PURPOSE: To prevent defects such as white dots and to obtain a sharp picture image even when a photosensitive material is used for a long period by specifying the temp. of dampining water, specifying the range of saturated water swelling of the photosensitive material and the image receiving material, and specifying the addition amt. of dampening water.

CONSTITUTION: The temp. of dampening water to be added to a heat developable photosensitive material having photosensitive silver halide, reducing agent, binder and dye-donating compd. is specified to ≥45°C. The saturated water swelling at this temp. of the dampening water is 10-20μm for the photosensitive material and 5-10μm for the image receiving material. The addition amt. of dampening water is specified to ≤90% of the sum of the saturated water swelling of the photosensitive material and image receiving material. When the temp. of dampening water is ≥50°C, the addition amt. of dampening water is ≤80% of the sum of saturated water swelling. The dampening water is added by passing the photosensitive material at a const. rate in a dampening water tank and successively removing the excess water on the surface of the photosensitive material with a nip roller. Thus, a const. amt. is always given.