An illuminating device in which one or more chamfer surfaces are formed at one or more corner portions, respectively, of a light guiding part, and a luminous body is disposed corresponding to a chamfer surface, and a display apparatus using the illuminating device are disclosed. The illuminating device has the light guiding part for guiding light to a display unit of the display apparatus and a light source part. The light guiding part includes an incident surface on which the light is incident, a back surface opposite to the incident surface, an emitting surface from which the light is emitted to the display unit, side surfaces perpendicular to the incident surface and the emitting surface, and chamfer surfaces formed at corner portions, respectively, each connected to the incident surface and one of the side surfaces. The light source part includes marginal luminous bodies each corresponding to each of the chamfer surfaces. The light source part may further have at least one central luminous body that corresponds to the incident surface.