1. An image forming apparatus, comprising: a first image forming unit that forms a first developer image with a first developer, a second image forming unit that forms a second developer image with a second developer that contains a larger amount of metal oxides having a low resistance than the first developer contains, a transfer part that contacts with the first image forming unit and the second image forming unit and transfers the first developer image and the second developer image to a transfer medium, a disjunction mechanism that moves the second image forming unit to realize a first state and a second state, the first state where both the first image forming unit and the second image forming unit contact with the transfer part and the second state where the second image forming unit separates from the transfer part and the first image forming unit contacts with the transfer part, a density detection part that detects densities of the first developer image and the second developer image transferred to the transfer medium, and a control part that controls operations of the first image forming unit, the second image forming unit, the transfer part, the disjunction mechanism, and the density detection part, wherein the control part controls an operation of the density detection part to cause the density detection part to detect a first density of the first developer image among the first developer image and the second developer image transferred to the transfer medium in the first state to obtain a first density detection result, and to detect a second density of the first developer image transferred to the transfer medium in the second state to obtain a second density detection result that is the density detection result, and afterwards computes a first density comparison value obtained by comparing the first density detection result with the second density detection result and corrects the density of the first developer image by subtracting the first density comparison value from the first density detection result.