An image forming apparatus comprising: a latent image bearer; an electrostatic latent image forming device (5, 20) to form an electrostatic latent image on the latent image bearer; a potential sensor to detect an electric potential on the latent image bearer; a toner image forming device to form a toner image based on the electrostatic latent image; a toner adhesion amount detector (48-1 to 48-4) to detect a toner adhesion amount of the toner image; and a control device to: control the electrostatic latent image forming device (5, 20) to create an adjustment pattern on the latent image bearer during a non-printing period when the image forming apparatus is not printing, control the potential sensor to detect an electric potential of the adjustment pattern, control the electrostatic latent image forming device (5, 20) and the toner image forming device to create a test toner image during a printing period, control the toner adhesion amount detector (48-1 to 48-4) to detect a toner adhesion amount of the test toner image, and adjust at least one image forming condition of the electrostatic latent image forming device (5, 20) and the toner image forming device based on the electric potential of the adjustment pattern and the toner adhesion amount of the test toner image, wherein the control device is configured to create a plurality of test toner images of different image densities in an unused area on the latent image bearer and adjust the image forming condition based on toner adhesion amounts of the plurality of test toner images, and wherein the adjustment pattern includes patches having the same image densities as the plurality of test toner images. a latent image bearer; an electrostatic latent image forming device (5, 20) to form an electrostatic latent image on the latent image bearer; a potential sensor to detect an electric potential on the latent image bearer; a toner image forming device to form a toner image based on the electrostatic latent image; a toner adhesion amount detector (48-1 to 48-4) to detect a toner adhesion amount of the toner image; and a control device to: control the electrostatic latent image forming device (5, 20) to create an adjustment pattern on the latent image bearer during a non-printing period when the image forming apparatus is not printing, control the potential sensor to detect an electric potential of the adjustment pattern, control the electrostatic latent image forming device (5, 20) and the toner image forming device to create a test toner image during a printing period, control the toner adhesion amount detector (48-1 to 48-4) to detect a toner adhesion amount of the test toner image, and adjust at least one image forming condition of the electrostatic latent image forming device (5, 20) and the toner image forming device based on the electric potential of the adjustment pattern and the toner adhesion amount of the test toner image, control the electrostatic latent image forming device (5, 20) to create an adjustment pattern on the latent image bearer during a non-printing period when the image forming apparatus is not printing, control the potential sensor to detect an electric potential of the adjustment pattern, control the electrostatic latent image forming device (5, 20) and the toner image forming device to create a test toner image during a printing period, control the toner adhesion amount detector (48-1 to 48-4) to detect a toner adhesion amount of the test toner image, and adjust at least one image forming condition of the electrostatic latent image forming device (5, 20) and the toner image forming device based on the electric potential of the adjustment pattern and the toner adhesion amount of the test toner image, wherein the control device is configured to create a plurality of test toner images of different image densities in an unused area on the latent image bearer and adjust the image forming condition based on toner adhesion amounts of the plurality of test toner images, and wherein the adjustment pattern includes patches having the same image densities as the plurality of test toner images.