A CCD laser displacement gauge is movable in three directions, that is, a vertical direction and two directions perpendicular to each other in a horizontal plane, and this gauge can be moved to a insulation displacement connecting center so as to detect a insulation displacement connecting height, the presence/absence of a wire, abnormal insulation displacement connection and a wire projecting amount. The insulation displacement connecting height, the wire presence/absence and the abnormal insulation displacement connection are detected by measuring a height of an upper surface of a wire sheath from a reference position at the position of the slot (at a middle position between two terminals if these terminals are juxtaposed). Whether or not the wire projecting amount is proper is determined by detecting the presence/absence of the wire at a position obtained by subtracting an absolute value of a tolerance from a normal projecting position. In the measurement, a waveform of a laser beam is sampled, and its peak is used as a measurement result. The CCD system detects the amount of light for each picture element, and even if there are variations in the surface condition of the wire which has just been insulation-displacement-connected, the position where the light amount is at a peak can be accurately detected.