Image forming apparatus

An image forming apparatus comprising:

• an image forming section having an image carrying member, the image forming section making the image carrying member carry an image formed with toner;
• an intermediate transfer belt being endless and having an outer circumferential surface to which the image is primarily transferred, the intermediate transfer belt rotating while carrying the transferred image;
• a primary transfer roller rotatable about an axis extending in a width direction orthogonal to a rotation direction of the intermediate transfer belt, the primary transfer roller being located inward, in the width direction, of an edge of the intermediate transfer belt in the width direction, the primary transfer roller being kept in pressed contact with the image carrying member across the intermediate transfer belt;
• a secondary transfer roller rotatable about an axis extending in the width direction, the secondary transfer roller forming a transfer nip with the outer circumferential surface of the intermediate transfer belt, the secondary transfer roller secondarily transferring the image to a sheet passing through the transfer nip;
• an image density sensor disposed at a distance from the outer circumferential surface of the intermediate transfer belt, the image density sensor shining light to the intermediate transfer belt to output a value corresponding to an amount of light reflected from the intermediate transfer belt;
• and
• a counter-sensor member disposed at an inner circumference side of the intermediate transfer belt, the counter-sensor member extending in the width direction so as to cross a position facing the image density sensor and making contact with the inner circumferential surface of the intermediate transfer belt,
• wherein
• when calibration is performed with respect to formation of the image, the image forming section, while primarily transferring to a transfer region on the intermediate transfer belt a print image to be secondarily transferred to the sheet, primarily transfers to a region outward, in the width direction, of the transfer region a test pattern image to be taken as a target of sensing by the image density sensor,
• when a dimension of the primary transfer roller in the width direction is represented by Wa, a dimension of the counter-sensor member in the width direction is represented by Wb, a dimension of the intermediate transfer belt in the width direction is represented by Wc, and a maximum dimension of the sheet in the width direction is represented by Wd, then a relationship Wd≤Wa<Wb≤Wc or a relationship Wd≤Wa<Wc≤Wb is fulfilled,
• a transfer position of the test pattern image is a position a predetermined distance away, inward in the width direction, from the edge of the intermediate transfer belt in the width direction, and
• the predetermined distance is twice or more a distance in the width direction from the edge of the intermediate transfer belt in the width direction to an edge of the primary transfer roller in the width direction.