A planar light source system having an LED (1) serving as a primary light source of substantially point-shaped light source, a light guide (2) having a light incident face on which light emitted from the LED (1) is incident and a light emission face (4) from which light guided through the light guide (2) is emitted, a light deflecting device (3) for controlling the direction of the emission light from the light guide (2), and a reflection sheet (6). LED (1) is disposed at a corner portion of the light guide (2), and many elongated prisms (5) are arranged substantially arcuately in parallel to each other on the light incident surface (14) of the light deflecting device (3) so as to surround LED (1).