1. An image forming apparatus comprising: an image forming unit that forms an electrostatic latent image on a photosensitive element by an electrophotographic process, and causes toner to adhere to the electrostatic latent image to form a visible image; and a control unit that controls the image forming unit, wherein at least a toner-adhesion-amount detector that detects a toner adhesion amount in an image-density-detection pattern image formed on the photosensitive element, an operating unit through which image formation is instructed, and a detection sensor that detects temperature and humidity in proximity of the image formation are connected to an input side of the control unit, at least a developing bias control unit that controls a developing-bias control condition in a developing process, a display unit that can display thereon a malfunction, and a communicating unit that displays a malfunction on an external device via a network are connected to an output side of the control unit, and the control unit compares changes of a toner adhesion amount in the image-density-detection pattern image when the developing-bias control condition is changed with respect to a toner adhesion amount in the image-density-detection pattern image in a normal status, performs a malfunction-occurrence prediction process according to a degree of each of the changes in density, and displays a result of the malfunction-occurrence prediction process.