1. An image forming apparatus, comprising: an image forming section which forms an image on a sheet; a reading section which reads the image formed by the image forming section over a predetermined width in a width direction of the sheet; a colorimeter which reads the image over a width smaller than the predetermined width in the width direction of the sheet; a calibration section which calibrates the reading section on the basis of a difference between first reading section measurement data and first colorimeter measurement data, the first reading section measurement data being obtained by reading an image for calibration formed on the sheet with the reading section, and the first colorimeter measurement data being obtained by reading the image for calibration with the colorimeter; a specification section which specifies adjacent images having a largest difference in brightness of a predetermined threshold value or more from among images for color adjustment formed on the sheet; and a color adjustment section which controls the colorimeter to read at least one of the adjacent images specified by the specification section and adjusts a color of the image formed by the image forming section on the basis of second colorimeter measurement data obtained by the colorimeter.