An image forming apparatus that can provide a quality image in a stable manner without lowering the productivity. A reference image forming unit forms reference images on a transfer member. A plurality of sensing units detect densities of the formed reference images. A control unit adjusts respective output values from the plurality of sensing units according to a difference between the output values from the plurality of sensing units. The control unit performs error processing according to the difference between the output values from the plurality of sensing units when the control unit adjusts the output values from the plurality of sensing units.