Light projecting device

A light projecting device comprising:

• a flat plate-shaped light guide plate and a light source body that introduces light from a side peripheral surface of the light guide plate to the inside thereof, wherein a plurality of concave parts are formed on a first plate surface of the light guide plate,
• the light guide plate is configured to reflect and spread the light entering the light guide plate is reflected at the concave parts, emit the light to the outside from a second plate surface of the light guide plate, and then irradiate the light to a predetermined object such that the object can be observed through the light guide plate from a side of the first plate surface of the light guide plate,
• the surface of each of the concave parts is formed with a smooth concave curved surface, and
• a tangential angle that is an angle between a tangential line at an opening edge of the concave part and the plate surface is set to be greater than or equal to 50° and less than or equal to 85° in a cross-sectional shape of the concave part cut by a plane that is both perpendicular to the plate surface and passing through the center of the concave part.