A light source unit, comprising: a light guide plate; a light source facing to a peripheral surface of the light guide plate; and a reflection part reflecting light emitted from one surface of the light guide plate, wherein the reflection part comprises: an elongated portion, which is positioned at an outside of an edge of the light guide plate, being elongated in a direction crossing the one surface; and a protrusion portion, which is located at a position of the elongated portion that is away from the one surface, protruding from the position to the one surface, wherein the one surface side of the light source is covered with the protrusion portion.