Image forming apparatus

An image forming apparatus, comprising:

• a photo conductor drum;
• a development roller configured to adhere toner to an electrostatic latent image on the photo conductor drum in order to develop a toner image;
• and
• a pattern image generating unit configured to develop two pattern images that are two sets of plural test patches for calibration on the photo conductor drum;
• wherein each one of the pattern images includes the test patches corresponding to densities in gradation;
• the pattern image generating unit is further configured to set an interval between a top of the first pattern image and a top of the second pattern image so that a remainder for the interval divided by a density fluctuation pitch is larger than a length of the test patch;
• and
• the density fluctuation pitch is the product of a periphery length of the development roller and a ratio between a rotating speed of the development roller and a rotating speed of the photo conductor drum.