An electronic component having connection terminals on one side thereof is bonded to a circuit board via an adhesive sheet having through-holes. The connection terminals on the electronic component are connected to electrode pads provided on the circuit board via a conductive adhesive in the through-holes. Thus, an electronic circuit device is formed. Using a polymeric resin film sheet for the circuit board and mounting an electronic component, e.g. an LSI, onto the circuit board can provide a small, light, thin, and inexpensive electronic circuit device.