An image forming apparatus includes an image bearer, a charging, a charge power supply to supply a charging bias to the charging device, a developing device, a toner adhesion amount detector, an environment detector, and a controller to determine whether to execute a charging bias adjustment process in which the charging device charges the image bearer to have different potentials, the developing device supplies the toner to the image bearer according to the different potentials, the toner adhesion amount detector detects the amount of toner adhering to the image bearer, and the controller adjusts the charging. The controller includes a memory device to store the environment data, and is configured to compare the environment data with previous environment data stored in the memory device, and determine not to execute the charging bias adjustment process when an environment change amount is not greater than a threshold.