an image forming apparatus includes a developing contrast voltage controller to control a developing contrast voltage so as to obtain a desired image density , a transfer condition controller to control transfer conditions for transferring a toner image , an environment sensor to detect an environment , and a correcting coefficient setting unit to refer to a database for pre - registering correcting coefficients to correct the transfer conditions corresponding to the developing contrast voltage and environment and set the correcting coefficients on the basis of the developing contrast voltage controlled by the developing contrast voltage controller and the environment detected by the environment sensor .