A receptacle includes a pair of spare terminals that are located on both sides of a plurality of receptacle terminals in a longitudinal direction and are short-circuited. A plug includes a pair of relay electrodes that respectively come in contact with the pair of spare terminals when the plug is connected to the receptacle. A connector inspection instrument includes a conduction detecting circuit and a pair of terminal support portions supporting a pair of inspection terminals, and a displacement mechanism. The displacement mechanism supports one or both of the pair of terminal support portions in such a way as to displace the one or both of the pair of terminal support portions in a width direction to narrow or widen an interval between the pair of inspection terminals.