A light source unit includes an attachment body including an attachment board, a circuit board having a first surface in contact with the attachment board and a second surface on which lighting sources are mounted. The light source unit further includes a cover attached to the attachment body so as to cover the second surface of the circuit board. The cover includes a panel covering the circuit board and a pair of inner flanges each of which extending from both ends of the panel in a width direction of the panel so as to come toward each other. The circuit board is supported by being held between the pair of inner flanges and the attachment board of the attachment body.