A highly reliable electronic circuit board for suppressing propagation of noise and a power line communication apparatus using it are provided. An electronic circuit board of the invention is connected to a different electronic circuit board and including a first board having a first face and a second face opposed to the first face and a second board having a third face and a fourth face opposed to the third face. The electronic circuit board includes a first circuit mounted on one end of the first face for performing analog signal processing; a second circuit mounted on another end of the first face for performing digital signal processing; a junction layer provided between the second face and the third face for jointing the first board and the second board; a built-in electronic component built into the junction layer; a connection part mounted on the fourth face and to be connected to the different electronic circuit board; and a first conducting path for electrically connecting the second circuit and the connection part, wherein the connection part is mounted at a position overlapping projection projecting the second circuit onto the fourth face from a vertical direction relative to the first face.