To stably maintain high image quality, by suppressing density fluctuation of a toner image patch, resulting from a fluctuation factor of the configuration of an apparatus.
A toner image 30 for detecting density fluctuation, which has a length equal to or greater than the circumferential length of a photoreceptor, is formed. The density of the toner image 30 for detecting density fluctuation is detected by a density sensor 43, and the periodicity of density fluctuation is detected. Then, in the position on the photoreceptor representing a predetermined density detection value, toner image patches P1, P2, and P3 are periodically formed by changing, with a multistage, an image forming condition that affects image density. The densities of them are detected by the density sensor 43 and an optimum image forming condition is set.
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