There is provided a light source unit including a light source case into which a plurality of optical members are incorporated, wherein the light source case has fixing portions for fixing the optical member which are provided in a position on a main body bottom plate of the light source case and in both side positions of the optical member above the main body bottom plate, and an upper fastening plate which presses down the optical member accommodated in the light source case, and wherein the fixing portions include a lower fixing portion where a primary positioning portion is formed on the main body bottom plate and side fixing portions where a pair of secondary positioning portions are formed which are brought into abutment with a surface of the optical member which is opposite to a surface thereof which is brought into abutment with the primary positioning portion.