Image forming apparatus

An image forming apparatus comprising:

• an image forming section that forms an image with toner;
• an intermediate transfer belt that is endless and that rotates while carrying on an outer circumferential surface thereof the image transferred from the image forming section, and
• a stretching roller that is rotatable about an axis extending in a width direction orthogonal to a rotation direction of the intermediate transfer belt, the stretching roller being disposed inward, in the width direction, of edges of the intermediate transfer belt in the width direction, the stretching roller having the intermediate transfer belt stretched thereon by making contact with an inner circumferential surface of the intermediate transfer belt,
• wherein
• the intermediate transfer belt
• has a printing region inward, in the width direction, of edges of the stretching roller in the width direction and
• has as a test region at least one of a pair of regions on both sides of the printing region in the width direction,
• the image forming section
• transfers to the printing region a print image to be printed on a sheet and
• transfers to the test region a test pattern image for calibration with respect to image formation by the image forming section,
• the image forming apparatus further comprises:
• an image density sensor that is disposed at a distance from an outer circumferential surface of the intermediate transfer belt, the image density sensor shining light to the test region to output a value corresponding to an amount of light reflected from the test region;
• and
• a counter-sensor member that makes contact with the inner circumferential surface of the intermediate transfer belt, the counter-sensor member having a counter portion facing the image density sensor across the intermediate transfer belt,
• edge positions of the counter portion in the width direction are inward, in the width direction, of edge positions of the stretching roller in the width direction or are same as the edge positions of the stretching roller in the width direction,
• the edge at one side of the stretching roller in the width direction is located inward, in the width direction, of the edge of the intermediate transfer belt at one side in the width direction and the edge at the other side of the stretching roller in the width direction is located inward, in the width direction, of the edge of the intermediate transfer belt at the other side in the width direction, and
• the image forming portion concurrently transfers the print image to the printing region and transfers the test pattern image to the test region.