The present invention provides an image forming apparatus having a conveying portion 8 includes a plurality of pre-fixing conveying belts 83 arranged in parallel to a width direction intersecting with the sheet conveying direction. The pre-fixing conveying belts convey a sheet to which a toner image is transferred by a fixing portion 9 to a fixing nip portion. The controlling portion controls a driving mechanism which moves at least one of the plurality of sheet conveying members and changes a projecting amount thereof with respect to the other sheet conveying member, and drives such that a conveying state of the pre-fixing conveying belt is obtained based on a state-setting table which is set according to type of sheet. It is possible to prevent sheet corrugated deformation as well as to solve a problem of generation of slip or distortion of a sheet caused by velocity difference between the driving portions.