A low cost image forming apparatus capable of detecting a moving speed or meandering of a revolving endless belt with high accuracy to thereby prevent the color shift includes: a revolving endless belt sequentially superimposing and transferring toner images formed on a plurality of photoconductive drums directly thereon or onto a recording sheet conveyed thereby; an emission part irradiating light to the endless belt; an image receiving part receiving light reflected on the endless belt to obtain successive images of the endless belt; and a control part comparing the successive images obtained by the image receiving part with one another, calculating either of a moving speed and an amount of meandering of the endless belt, and correcting either of the moving speed and the meandering of the endless belt based on a result of the calculation.