1. An image forming apparatus, comprising: a latent image bearer to bear a latent image on a surface thereof; a latent image forming device to form the latent image on the surface of the latent image bearer; a developing device including a developer bearer, to develop the latent image with toner carried on the developer bearer; a driving device to drive the latent image bearer and the developer bearer together and individually; a transfer body onto which toner on the surface of the latent image bearer is transferred; a toner detector to detect a toner adhesion amount of toner adhered to one of the surface of the latent image bearer and a surface of the transfer body; an error notification device to notify a user of occurrence of error; and a controller to control the toner detector to detect, at a preparation running and while the driving device drives the latent image bearer, one of a toner adhesion amount at a background portion of the latent image bearer and a toner adhesion amount at a background corresponding region of the transfer body in a toner adhesion amount detection, and to control the error notification device to notify the user of occurrence of abnormality in an error notification in a case in which the toner adhesion amount detected in the toner adhesion amount detection is equal to or greater than a predetermined threshold value, the controller controlling the driving device to stop only the developer bearer after driving both the latent image bearer and the developer bearer at the preparation running, but before a trailing edge of a detection target region of one of the background portion of the latent image bearer and the background corresponding region of the transfer body, at which the toner adhesion amount is detected, advances to an opposite position to the toner detector.