Light guide plate, light source device, and display device

A display apparatus comprising:

• a light guide plate which has a flat-plate member provided with a first surface including a flat surface portion and a recessed portion in a conic-like solid shape and a second surface opposed to the first surface, the flat-plate member configured to receive light from the recessed portion, to propagate the light inside the flat-plate member while diffusing the light, and to radiate the diffused light from the second surface, wherein an angle between an inclined surface of the recessed portion and a normal line to the flat surface portion is smaller than a value obtained by calculation in which twice a critical angle where the light is totally reflected by the second surface inside the flat-plate member is subtracted from 90°;
• a light source provided below the recessed portion and configured to emit light which enters the light guide plate from the recessed portion;
• and
• a display unit configured to display by using a light source device having said light guide plate and said light source.