In a light guide unit (40) of the present invention, a light source (22) is provided on a first end section (24d) of a light guide (24). Further, a side reflective member (26b), which can reflect light in the light guide (24), is provided on a second end section (24e) opposite to the first end section (24d) which is provided with the light source (22). The light guide (24) is continuously increased in thickness (D2, D4, and D5) (i) from the first end section (24d) provided with the light source (22) toward a center of the light guide (24) and (ii) also from the second end section (24e) provided with the side face reflective member (26b) toward the center of the light guide (24).