1. An image forming method comprising: forming an electrostatic latent image on an electrostatic latent image carrier; forming a toner image of the electrostatic latent image on the electrostatic latent image carrier; transferring the toner image to an intermediate transfer member by forming an electric field between the electrostatic latent image carrier and the intermediate transfer member; first detecting an image density of an image that is transferred using a predetermined reference electric field; second detecting an image density of the image that is transferred using an electric field that is smaller or greater than the reference electric field; determining a level of degradation of a degraded toner based on the image density detected by each of the first detecting and the second detecting; and determining to perform a processing of the degraded toner based on a comparison of a predetermined threshold with a value determined from the image density detected by the first detecting and the image density detected by the second detecting.