PURPOSE: To achieve simple assembly of a wiring board to be accommodated in a casing of an electronic circuit unit designed in small length and thickness.

CONSTITUTION: A heat generating electronic part 12 is loaded at the surface of a heat sink plate 1 and a conductive lead is projected at the end faces in the upper and lower directions of the heat sink plate 1. Circuit wiring substrates 5, 6 are connected and integrated by soldering through connection of the heat sink plate 1 between the wiring boards 5 and 6 mounting many electronic parts. With this connection, the wiring boards 5, 6 are coupled rigidly in U-shape and electrical connection between both wiring boards 5, 6 can be realized by connecting the projected lead portions 3 with a part of the circuit wirings of the wiring boards 5, 6. Therefore, assembly of wiring boards to be accommodated into the casing of an electronic circuit unit which is designed in small length and thickness can be attained simply by utilizing a heat sink plate as a part of the wiring pattern.