Abstract: An electronic device comprises a substrate having electronic parts, electric conductive wires for electrically connecting between the electronic parts, a front surface on which the electronic parts and electric conductive wires are mounted, a reverse surface and at least one electronic part back portion opposite to the electronic parts; and at least one high thermal conductivity member, a thermal conductivity coefficient thereof being higher than that of the substrate, the high thermal conductivity member being connected to the electronic part back portion while the high thermal conductivity member is opposite to the electronic parts in a substrate width direction to decrease a difference in temperature between the electronic parts.