Disclosed is an image forming apparatus including a color converter for converting cyan, magenta and yellow components of a first image signal to equivalent neutral density, calculating a first gray component from cyan, magenta and yellow components of equivalent neutral density, subtracting the first gray component from each of the cyan, magenta and yellow components of equivalent neutral density, subjecting each of the cyan, magenta and yellow components of equivalent neutral density from which the first gray component is subtracted to an inverse conversion of the equivalent neutral density conversion, and outputting a second image signal comprising cyan, magenta and yellow components which are obtained by carrying out the inverse conversion to the cyan, magenta and yellow components of equivalent neutral density from which the first gray component is subtracted, the first black component and the first gray component; an image forming section for forming an image on a paper based on the second image signal by using cyan, magenta, yellow, black and gray toners; and a controller for controlling the color converter and the image forming section.