A light guide emits lights incident on an end face from an emitting face
extending longitudinally of the guide, while having the lights reflected
by its internal face. A sectional shape of the guide in a direction
orthogonal to the longitudinal direction of this light guide has two
opposite parabolas, a line segment connecting the focal points of the two
opposite parabolas, and a line segment (bottom face) corresponding to the
emitting face. A scattering pattern consisting of white ink is formed on
the line segment (bottom face) connecting the focal points. With this
guide, the face of a document is to be efficiently illuminated by
conversely utilizing the characteristic of the compound parabolic
concentrator (CPC) to convert scattered lights extending over a full
angle from a limited area into radiant lights confined to a prescribed
emission angle and thereby minimizing the expansion of lights.