An image forming apparatus comprising: a first image carrier which allows a toner image to be formed thereon; a plurality of second image carriers(2a,2b,2c) each of which allows a toner image to be formed thereon; a transfer belt of endless belt type, which allows the toner images formed on the first image carrier and/or the second image carriers(2a,2b,2c) to be transferred onto the transfer belt; a drive roller which supports the transfer belt in a rotatable manner and is capable of rotating the transfer belt; a driven roller which supports the transfer belt in a rotatable manner; a first opposing portion which is provided opposing to the first image carrier via the transfer belt and causes the transfer belt to contact the first image carrier; a plurality of second opposing portions(13a,13b,13c) which are provided opposing to the plurality of second image carriers(2a,2b,2c) via the transfer belt and are each capable of being positioned at either contact positions that cause the transfer belt to contact the plurality of second image carriers(2a,2b,2c) or separation positions that cause the transfer belt to be separated from the plurality of second image carriers(2a,2b,2c); a movement mechanism portion which is able to move the positions of the plurality of second opposing portions(13a,13b,13c) to the contact positions or the separation positions; position information acquiring portion which is able to acquire position information with respect to a width direction about the transfer belt; a roller position adjustment mechanism which is able to adjust the orientation of a rotary shaft of the driven roller; a first control portion which is configured to determine correction information for returning the transfer belt to a predetermined target position, based on the position information about the transfer belt acquired by the position information acquiring portion, and is configured to control the roller position adjustment mechanism based on the correction information; characterised by a second control portion which, in the case where, during the control for the roller position adjustment mechanism based on the correction information by the first control portion, the transfer belt does not return into a correction range centered on the target position within a predetermined time and is out of the correction range, is configured to control the movement mechanism portion so as to change the positions of the plurality of second opposing portions. a first image carrier which allows a toner image to be formed thereon; a plurality of second image carriers(2a,2b,2c) each of which allows a toner image to be formed thereon; a transfer belt of endless belt type, which allows the toner images formed on the first image carrier and/or the second image carriers(2a,2b,2c) to be transferred onto the transfer belt; a drive roller which supports the transfer belt in a rotatable manner and is capable of rotating the transfer belt; a driven roller which supports the transfer belt in a rotatable manner; a first opposing portion which is provided opposing to the first image carrier via the transfer belt and causes the transfer belt to contact the first image carrier; a plurality of second opposing portions(13a,13b,13c) which are provided opposing to the plurality of second image carriers(2a,2b,2c) via the transfer belt and are each capable of being positioned at either contact positions that cause the transfer belt to contact the plurality of second image carriers(2a,2b,2c) or separation positions that cause the transfer belt to be separated from the plurality of second image carriers(2a,2b,2c); a movement mechanism portion which is able to move the positions of the plurality of second opposing portions(13a,13b,13c) to the contact positions or the separation positions; position information acquiring portion which is able to acquire position information with respect to a width direction about the transfer belt; a roller position adjustment mechanism which is able to adjust the orientation of a rotary shaft of the driven roller; a first control portion which is configured to determine correction information for returning the transfer belt to a predetermined target position, based on the position information about the transfer belt acquired by the position information acquiring portion, and is configured to control the roller position adjustment mechanism based on the correction information; characterised by a second control portion which, in the case where, during the control for the roller position adjustment mechanism based on the correction information by the first control portion, the transfer belt does not return into a correction range centered on the target position within a predetermined time and is out of the correction range, is configured to control the movement mechanism portion so as to change the positions of the plurality of second opposing portions.