Backlight having light guide plate with side surface with inclination angle and image display device

A backlight comprising:

• a light guide plate having a first main surface, a second main surface opposite the first main surface, and a side surface connecting the first main surface and the second main surface, the side surface having a first region and a second region different from the first region;
• and
• a light emitting element that emits light toward the first region of the side surface of the light guide plate,
• the side surface of the light guide plate including, in the second region of the side surface of the light guide plate, a first inclined surface that extends from an outer edge of the first main surface in an inclined manner and has an inclination angle between 52° and 70° with respect to the first main surface such that there is an increased light utilization efficiency effect of the light guide plate,
• the light guide plate being formed in a rectangular shape,
• the first region of the side surface of the light guide plate being disposed corresponding to one edge of the light guide plate, and
• the second region of the side surface of the light guide plate being disposed corresponding to the other three edges of the light guide plate.