Surface light source device includes: point light sources (13); light guide plate (1) having (i) two end parts in length direction, one of which serves as incident surface (2), and (ii) two end parts in thickness direction which serve as exit surface (7) and back surface (8), light guide plate (1) directing light, emitted from point light sources (13), incident on incident surface (2), so as to cause light to exit from substantially entire area of exit surface (7); and reflector (14) which reflects, toward incident surface (2), part of light which is emitted from point light sources (13) and is then reflected from incident surface (2). Incident surface (2) has elliptic arc (10) which is concave part having surface shape along elliptic arc identical to elliptic arc which is part of ellipse (31) having two focal points corresponding to point light sources (13) and reflector (14). Point light sources (13) and reflector (14) are provided on ellipse focal point lines (11 and 12) obtained by moving two focal points in width direction of light guide plate (1).