A light source apparatus include a light guide plate, a plurality of optical sheets and a frame, wherein one of the optical sheets is a prism sheet having a plurality of prisms on one surface and one or more integrally formed dark part suppressing projecting pieces engaging the frame. A pair of dark part suppressing sides adjoin the dark part suppressing projecting piece and form a first angle equal to or smaller than a dark part suppressing angle. Second angles making a pair of angles formed with a straight line and each of dark part suppressing sides are equal to or smaller than half of the dark part suppressing angle. The straight line passes through a region formed between the pair of dark part suppressing sides, passes through an intersection point of the pair of dark part suppressing sides and is parallel or perpendicular to ridge lines of the prisms.