PURPOSE: To obtain a coupling structure in which electronic components can be mounted at high density and whose space utilization efficiency is enhanced by a method wherein a connection means which electrically connects and mechanically fixes a plurality of main printed-circuit boards and a plurality of sub-printed-circuit boards is installed in the coupling part of the main printed-circuit boards to the sub-printed- circuit boards.

CONSTITUTION: Fitting receiver parts 8 are formed of box-shaped protrusion parts provided with opening parts whose size corresponds to that of salient connection parts 6, and conductor parts which connect conductor parts 7 electrically are exposed on inner faces of the box-shaped protrusion parts. In addition, coupling mechanisms which are detachable by fitting recessed parts to protruding parts are installed at fitting parts of the salient connection parts 6 to the fitting receiver parts 8 so as to surely maintain the fitting state (the mechanical union state) of the salient connection parts 6 to the fitting receiver parts 8. Then, when the salient connection parts 6 are fitted to the fitting receiver parts 8, a plurality of main printed-circuit boards 1, 2 and a plurality of sub-printed-circuit boards 3, 4 are coupled to be a box-shaped structure, and the individual printed-circuit boards are united mechanically with each other and connected electrically.