An image developing method is disclosed that is able to efficiently remove degraded toner on a developing agent carrier, prevent formation of abnormal images, ensure good image quality over time, and increase the service life of the device. The developing method includes a step of calculating an amount of consumption of the developing agent during image formation and an amount of consumption of the developing agent in a compulsory toner consumption mode under different calculation conditions between the image formation and the compulsory toner consumption mode. In the compulsory toner consumption mode, a developing bias different from a developing bias used during image formation is applied for a predetermined time period to discharge residual developing agent on a developing agent carrier to a latent image carrier.