Light-guiding body, light-guiding body fabrication method, optical shutter, and planar light source device

[Problem] To provide a light-guiding body whereby it is possible to configure an optical shutter having high translucence in a shutter open state, and having a high shielding function in a shutter closed state. [Solution] Provided is a plate-shaped light-guiding body (4) wherein two facing primary faces are light-emitting faces (6A, 6B), and at least one lateral end face is a light-entry face (5). Light-emitting mechanisms (6) are formed in a region of at least a portion of at least one of the primary faces. A haze value in the region wherein the light-emitting mechanisms are formed is 3% or less. When a completely diffuse light from at least one of the light-entry faces (5) has entered, angles (thetaA, thetaB), whereat the intensity of emitted light (8) from the primary faces is at maximum, are in a range of -60 DEG - +60 DEG about a normal of the primary faces, and emitted light efficiency is 15% or more.