Image forming apparatus

An image forming apparatus comprising:

• an image carrier configured to carry a toner image;
• an image forming unit configured to form the toner image on the image carrier;
• an intermediate transfer belt on which the toner image formed on the image carrier is transferred;
• a transfer member configured to transfer the toner image transferred on the intermediate transfer belt on a recording medium;
• a power supply configured to apply a transfer voltage to the transfer member;
• a sensor configured to detect the toner image formed on the recording medium;
• and
• a control unit configured to execute an adjustment mode for adjusting the transfer voltage to be applied to the transfer member in transferring the toner image from the intermediate transfer belt on a recording material during non-image formation,
• wherein, in the adjustment mode, the control unit controls the power supply to transfer a plurality of test toner images to the recording material by applying a plurality of levels of test voltages to the transfer member, and adjusts the transfer voltage to be applied to the transfer member based on a detection result of detecting the plurality of test toner images by the sensor, and
• wherein, in the adjustment mode, the control unit (i) sets a plurality of groups consisting of test toner images extracted from the plurality of test toner images, (ii) acquires an index value for each of the plurality of groups based on the detection result of detecting the plurality of test toner images by the sensor, (iii) extracts a specific group from the plurality of groups based on the index value, (iv) extracts a specific test toner image from test toner images included the specific group, and (v) adjusts the transfer voltage to be applied based on a test voltage of the specific test toner image.