PURPOSE: To form an image with high resolution on the I/O terminal of each electronic circuit substrate by constituting an image forming network bidirectional to/from a multistage conjugate image forming face.

CONSTITUTION: A straight groove is formed between the end faces of respective rod lenses 2 and the end part of an electronic circuit substitute 5 can be inserted into the groove. The end part of each substrate 5 is provided with a transmission type spatial modulation element(SLM) 6 and a transparent type optical sensor array 7, and at the time of inserting the end part of the substrate 5 into the groove, the SLM 6 and the array 7 are positioned on the conjugate image forming face of both the rod lenses 2. When plural circuit substrates 5 are inserted into respective conjugate image forming face positions I1 to I5, optical pattern information generated from the SLM 6 of an optional substrate 5 can be simultaneously detected by the optical sensor arrays 7 of all the other circuit substrates 5.