PURPOSE: To provide an image stabilizing method for a full-color copying machine capable of obtaining a stable full-color image without color difference on every sheet.

CONSTITUTION: When a power is supplied, a preliminary operation processing for warming up a fixing device is executed (S1), and when a temperature is ≤70°C, a test mode is applied (S2), and the initialization in a memory is performed (S3). At this time, toner images (monochromatic color) are formed on the surfaces A and B of a photosensitive body (S4). The toner images formed on the surfaces A and B of the photosensitive body are respectively detected by a photosensor so as to perform an arithmetic operation and calculate density DA and density DB (S5). In the case that the density DB is low as compared with the density DA regarded as the reference (S6), a potential correction and a light quantity correction with reference to a difference between the density and the density DB is performed so as to increase a processing condition on the surface B of the photosensitive body (S7 and S8). In the case that the density DB is higher than the density DA, the potential correction and the light quantity correction with reference to the difference between the density DA and the density DB are performed so as to decrease the processing condition on the surface B of the photosensitive body (S9 and S10).