To check a steep rise in device cost and any possible enlargement of a device as well as to widen the range of option device selectiveness by using a paper conveying pass for a duplex unit equipped by an image former combinedly with another paper feed conveying pass of a paper feed option unit, and connecting the duplex unit and the paper feeding unit to each other freely in compliance with the desire.

An image former 101 is provided with an installing part 120 capable of installing either of a duplex unit or a paper feeding unit 102 selectively. In addition, this time former 101 is equipped with a paper feeding pass 118 to guide a sheet of paper to be fed out of the duplex unit being installed up to a register sensor 109. The paper feeding unit 102 is connected to the image former 101 with the installing part 120 to install the duplex unit and a connector or the like. In succession, in time of paper feeding, the paper feeding pass 118 is used. Then, coupling connector, at the side of the image former 101, connecting a control bus bar and this image former 101 is combined with the coupling connector connecting this control bus bar of the duplex and the image former 101 to each other, jointly.