To provide a tandem type color image forming apparatus capable of effectively preventing color shift by restraining variation in the rotating speed of an intermediate transfer belt by a simple configuration.

The pressure contact force (a) applied to a photoreceptor drum 1d by a primary transfer roller 6d closest to a secondary transfer roller 9 among primary transfer rollers 6a to 6d disposed in pressure contact with photoreceptor drums 1a to 1d respectively via the intermediate transfer belt 8 is increased within a range that does not exceed two times the pressure contact force (b) applied to each of the photoreceptor drums 1a to 1c by the other primary transfer rollers 6a to 6c respectively.