1. An image forming apparatus comprising: an image forming part, which forms an image in any one of a plurality of image forming modes with respectively different processing speeds; and a density calibration control part, which performs image density control for said image forming part in a state where any one of the plurality of image forming modes is applied, wherein said density calibration control part makes a performing time interval for the image density control in a first image forming mode and a performing time interval for the image density control in a second image forming mode different from each other.