A smooth mating operation is enabled by a simple configuration in a state in which electric connectors are easily and reliably positioned. A plug-side mating guide member made of metal projecting to an outer side from a wiring substrate is provided with guide surfaces, which contact part of a counterpart connector and slide so as to carry out positioning of a mating operation. Apart from which the plug-side mating guide member projects from the wiring substrate is directly or indirectly checked visually. As a result, the mating operation can be carried out while approximating the mutual mating positional relation of both of the electric connectors, and the mating positional relation is regulated to a predetermined state by guiding actions of the guide surfaces of the plug-side mating guide member so that the mutual mating operation of the electric connectors is easily and precisely carried out.