A signal input/output device includes an array of signal input/output units. The signal input/output units have respective bases, each of which includes a connecting member. The connecting member has a second protruding end finger swingably supported on a base, and a first protruding end finger that engages with a stop of an adjacent base. The connecting member is positioned and fixed (secured) by a screw, which extends through a bottom plate and is threaded in a square nut. The connecting member, when secured in this manner, joins the adjacent bases to each other.