An output-noise reduction device configured to reduce noise mixed in an output signal output from an electronic device accommodated in a metal casing to a supplying device, the output-noise reduction device comprising: a conducting bar (11, 11A, 11B, 111, 112, 113, 114, 115) that is made of a conductive material, and has one end portion serving as a connection terminal to be connected to an output end of the electronic device, and another end portion serving as an output terminal; a first magnetic body core (13, 13A, 131, 132, 133) that is made of a magnetic material and includes a through hole (13a, 13Aa, 131c, 132c, 133c) through which the conducting bar is inserted; a molded member (23, 23A, 23B, 23D) that is made of a resin material and encapsulates a portion of the conducting bar excluding the connection terminal and the output terminal and encapsulates the first magnetic body core; and a first mounting board (17, 17A, 17B) that is encapsulated by the molded member, and includes: a first fixing portion (31, 31A, 31B) fixed to a portion of the conducting bar between the first magnetic body core and the output terminal; a second fixing portion (33, 33A, 33B) configured to be connected to the metal casing; and a connecting portion (35, 35A, 35B) with a capacitive element connecting between the first fixing portion and the second fixing portion, wherein a section from the output terminal to at least part of the capacitive element mounted on the first mounting board is configured to be isolated from electromagnetic coupling from the electronic device, wherein the first fixing portion is electrically connected to the conducting bar and to the capacitive element, and the second fixing portion is electrically connected to the capacitive element and configured to be electrically connected to the metal casing; and the first mounting board is made of a highly conductive metal material. a conducting bar (11, 11A, 11B, 111, 112, 113, 114, 115) that is made of a conductive material, and has one end portion serving as a connection terminal to be connected to an output end of the electronic device, and another end portion serving as an output terminal; a first magnetic body core (13, 13A, 131, 132, 133) that is made of a magnetic material and includes a through hole (13a, 13Aa, 131c, 132c, 133c) through which the conducting bar is inserted; a molded member (23, 23A, 23B, 23D) that is made of a resin material and encapsulates a portion of the conducting bar excluding the connection terminal and the output terminal and encapsulates the first magnetic body core; and a first mounting board (17, 17A, 17B) that is encapsulated by the molded member, and includes: a first fixing portion (31, 31A, 31B) fixed to a portion of the conducting bar between the first magnetic body core and the output terminal; a second fixing portion (33, 33A, 33B) configured to be connected to the metal casing; and a connecting portion (35, 35A, 35B) with a capacitive element connecting between the first fixing portion and the second fixing portion, wherein a section from the output terminal to at least part of the capacitive element mounted on the first mounting board is configured to be isolated from electromagnetic coupling from the electronic device, wherein the first fixing portion is electrically connected to the conducting bar and to the capacitive element, and the second fixing portion is electrically connected to the capacitive element and configured to be electrically connected to the metal casing; and the first mounting board is made of a highly conductive metal material.