In an attachment structure for attaching an attached-plate to a printed substrate which is installed in a mechanical chassis, the mechanical chassis includes a positioning pin for positioning the printed substrate; and the attached-plate includes a guide groove that engages with the positioning pin and is slidably guided in a predetermined path, a fixing portion to the printed substrate, and an engaging portion that engages with a side portion of the printed substrate. By causing the attached-plate to slide along a substrate side of the printed substrate with the guide groove being engaged with the positioning pin, the guide groove is guided by the positioning pin, whereby the engaging portion engages with the side portion of the printed substrate. In the engagement state, by fixing the fixing portion of the attached-plate to the printed substrate, the attached-plate is attached to the printed substrate.