Patent ID: 7333759

Claim:
An image forming apparatus comprising: photosensitive drums on which an image is formed; a transfer belt which moves while contacting or separating from the surfaces of the photosensitive drums; primary transfer rollers which are provided at the positions opposite to the photosensitive drums, moved to the transfer belt to make the transfer belt contact with the photosensitive drums, and transfers the images on the photosensitive drum to the transfer belt; a secondary transfer roller which transfers the images transferred to the transfer belt to a paper sheet; and a transfer roller drive unit which has an all-contact mode to move all the primary transfer rollers to the transfer belt and make the transfer belt contact with all the photosensitive drums, and an all-separate mode to move all the primary transfer rollers to the opposite side of the transfer belt, and separate the transfer belt from all the photosensitive drums, and a partial contact mode to move only some primary transfer rollers to the transfer belt and make the transfer belt contact with the some primary transfer rollers, and sets the all-separate mode after the all-contact mode, sets the partial contact mode after the all-contact mode, and sets the all contact mode after the partial contact mode.