Image forming apparatus, and control method for the same

An image forming apparatus comprising:

• a photosensitive member;
• a developing roller configured to supply a developer to the photosensitive member;
• a belt to which a developer image formed by the developer is to be transferred from the photosensitive member;
• a sensor configured to detect a density of the developer image on the belt;
• and
• a controller configured to execute a developing bias correcting process for correcting a developing bias to be applied to the developing roller:
• wherein the developing bias correcting process includes:
• a setting process for setting a plurality of testing biases to be applied to the developing roller, all of the plurality of testing biases being smaller than an old developing bias used for forming an image on a sheet before executing the developing bias correcting process;
• a forming process for forming a plurality of developer images on the belt by using the plurality of testing biases set in the setting process;
• a detecting process for detecting densities of the plurality of developer images formed in the forming process by the sensor;
• and
• a calculating process for calculating the developing bias based on the densities of the plurality of developer images detected in the detecting process.