There is provided a spread illuminating apparatus including an LED, a light guide plate and a flexible printed circuit board on which the LED is mounted, wherein the light guide plate includes: a light entrance end surface at which the light source is disposed; a light emitting portion from which light emitted from the light source and introduced into the light guide plate exits out in a spread manner; a slope portion which is disposed between the light entrance end surface and the light emitting portion and which has a thickness decreasing toward the light emitting portion; and a seat block disposed at the slope portion and configured to fixedly receive the flexible printed circuit board. In the spread illuminating apparatus, the length of the slope portion is substantially 1.78 times as large as the largest thickness of the slope portion.