To enable even a user, who works for the first time, to fix a unit to the surface of a device body readily and safely by using a connection member.

A connection member 52 is provided with a fixing part 58 which is prepared by bending a board material and fixed to a printer device body, a pad part 59 for mounting the double-sided unit temporarily when the double-sided unit (a unit to be attached to the surface of the device) is fixed to a device body and a supporting pin (rotating locking part) 60 which locks into to a pin hole (rotating locking part) at the double-sided unit side when the double-sided unit mounted on the pad is slid. A drop-out prevention member 62 consisting of a plate spring is attached on a pad part by welding or the like. When a double-sided unit is mounted on a pad part temporarily, a drop-out prevention member moves against elasticity by pressing the double-sided unit, and when the mounted double-sided unit is slid, locking to the double-sided unit is released and it returns based on elasticity, thus preventing return of the double-sided unit.