Planar illumination device

A planar illumination device comprising:

• a light guide plate formed by arranging a plurality of unit light guide plates each having a light emission surface as a front surface and a reflection surface as a back surface so that mating end surfaces of adjacent unit light guide plates of the plurality of unit light guide plates are closely arranged;
• and
• one or two or more light sources arranged on a side surface other than the mating end surfaces of adjacent light guide plates, of each of the plurality of unit light guide plates,
• wherein a projection section is arranged on one of mating surfaces of two adjacent unit light guide plates in the arrangement direction, and the projection section is matable with a recession section that is arranged on the other of the mating surfaces of the two adjacent unit light guide plates, and
• wherein the projection sections and recession sections are configured such that when adjacent unit light guide plates are closely arranged there is a gap between a lower surfaces of the projection sections and an upper surfaces of the recession sections.