The light source unit includes: a semiconductor light emitting element; a lighting circuit configured to operate the semiconductor light emitting element; a first heat dissipation plate on which the semiconductor light emitting element is placed; a second heat dissipation plate on which the lighting circuit is placed; a wiring member electrically interconnecting the semiconductor light emitting element and the lighting circuit; and an interconnection member to which the first heat dissipation plate and the second heat dissipation plate are attached. The interconnection member is lower in thermal conductivity than the first heat dissipation plate and the second heat dissipation plate.