An electronic component (chip) mounted structure includes a chip having a terminal, a wiring board having a terminal electrically connected to the terminal of the chip, and an interposing board disposed between the chip and the wiring board and having a structure including an insulating base material provided with a large number of filamentous conductors penetrating the insulating base material in a thickness direction thereof. The terminal of the chip is electrically connected to the terminal of the wiring board via a plurality of filamentous conductors provided in the interposing board.