A light source unit is provided with a housing, a substrate, and light-emitting devices. The light-emitting devices are mounted on a mounting part of the substrate. A heat dissipation part extends from an outer edge of the mounting part in a direction opposite to a light emitting direction of the light-emitting devices. The mounting part is held on a bottom part of the housing. A peripheral groove part extends in the direction opposite to the light emitting direction along an outer edge of the bottom part. The heat dissipation part is accommodated in the peripheral groove part.