When the dimension of a primary transfer roller in the width direction is represented by Wa, the dimension of a counter-sensor member in the width direction is represented by Wb, the dimension of an intermediate transfer belt in the width direction is represented by Wc, and the maximum dimension of a sheet in the width direction is represented by Wd, then the relationship WdWa<WbWc is fulfilled. The transfer position of a 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. The predetermined distance is twice or more the distance in the width direction from the edge of the intermediate transfer belt in the width direction to the edge of the primary transfer roller in the width direction.