Provided are an image forming apparatus, a fixing device, and an image forming system using the same, including: an image forming section for transferring a toner image onto a recording sheet; a first and second fixing rollers for thermally fixing the toner image on the recording sheet; a first and second temperature sensors each provided at a plurality of positions in a longitudinal direction of the fixing roller; and a rocking section for reciprocally shifting at least one of the fixing rollers in the longitudinal direction of the fixing roller, wherein the temperature gradient of each of the fixing rollers is detected, a central position of reciprocal shift of one fixing roller which can be shifted is set such that the temperature gradient of the other fixing roller is cancelled, and then the one fixing roller is reciprocally shifted by the rocking section.