1. A double-sided image formation system, comprising: two image formation sections, each image formation section having an image support transporter wherein images are supported and transported on each said image support transporter, to transfer the images on each said image support transporter to both sides of a recording medium and forming the images thereon; and density sensing means for sensing a density of said image, during which said image is being transferred from one of said two image formation sections to said image support transporter in another image formation section of said two image formation sections; each said image support transporter faces each other in said two image formation sections, each image support transporter comprising, an image formation support for forming and supporting each image formed thereon, and an intermediate transfer body facing said image formation support where said image formed on said image formation support is temporarily transferred to said intermediate transfer body; density sensing means for secondary transfer for sensing a density of an image transferred from said intermediate transfer body in said one image formation section to said intermediate transfer body in said another image formation section; and density sensing means for primary transfer for sensing a density of a primarily transferred image on each said intermediate transfer body.