PURPOSE:To enable the high-density mounting with facility of exchange and interconnection of wiring board or the like by arranging plural flat-plate form circuit board on which LSIs are mounted on the multilayer printed wiring board vertically, which are connected by plural multielectrode conectors. CONSTITUTION:The mutlielectrode connectors 51 and 51' in which contact springs 23 and 24 are built-in are arranged on the upper side of the multilayer printed wiring board 2 and the circuit board 8 on which LSIs 9 are mounted is inserted in the connector 51 so as to stand upright on the wiring board 2 and to bring terminals 12 and 13 of the cirlcuit board 8 in contact with the springs 23 and 24. The similar circuit board 8' is inserted into the connector 51' and heat sinks 10 and 10' on the back of the circuit board are arranged oppositely to each other. A connector 41 having a flat cable is inserted into the top of the circuit board 8 to bring the terminals 43 and 42 in contact with springs 21 and 22 of the connector. The similar connector 41' is inserted into the circuit board 8' and interconnection is done. Consequently, plurality of block mounting structures composed of the cirlcuit board, the connector with a cable and the multielectrode connectors can be formed on the wiring board 2 and exchange and connection are facilitated as well as the LSIs can be mounted with high density.