An image forming apparatus includes a duplex conveyance path where a recording medium can be reversed and re-fed; and an output image detector to detect an image or a test pattern formed on a surface of the recording medium. The image forming apparatus is configured to: detect the test pattern formed on the first side of the recording medium by the output image detector; adjust and correct image forming conditions based on the detection result of the detector; convey the recording medium the first side of which the test pattern is formed on, to a duplex conveyance path; re-feed the recording medium and form a test pattern for verifying correction effect on a backside of the recording medium after correcting and updating the image forming conditions; and detect the test pattern formed on the backside of the recording medium again by the output image detector, thereby verifying the correction effect.