IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an image forming apparatus that employs an intermediate transfer tandem system for arranging a plurality of primary transfer means in parallel and simultaneously applying bias from a single power source to the plurality of primary transfer means, and suppresses power consumption even when a bias value of a primary transfer bias needs to be changed at some point during continuous printing or double-sided printing, for example when there are multiple types of recording media, and thereby maintains image quality to ensure productivity of image formation.SOLUTION: During continuous printing or double-sided printing, a prescribed control bias, which is changed by detection of a recording medium that is different in type from a recording medium that is initially detected, is applied after the final color toner image before the application of the prescribed control bias is primary-transferred.