PURPOSE: To make it possible to easily detect the presence and absence of the detachment of connection pins, by collectively connecting a connector, which has electrical contacts at every connection pin mounted to the through-hole parts provided to a printed board being a back panel, to said connection pins.

CONSTITUTION: A conductive rubber sheet 11 is provided to the end parts of the insert holes 10 provided to a connector 9 made of a synthetic resin, of which the insert holes 10 are engaged with a large number of connection pins 4 mounted to a printed board 1 being a back panel capable of easily insert said connection pins 4, and contacts 12a, 12b are provided so as to obtain a gap of about 0.5mm from the conductive rubber sheet 11. In the next step, the insert holes 10 of the connector 9 are engaged with a large number of the connection pins 4 mounted to the printed broad 1 which must be subjected to the detection of the detachment of the connection pins 4. By collectively inserting the connection pins 4 mounted to the printed board 1 as mentioned above, the presence and absence of the detachment of the connection pins can be detected.