Light source device

A light source device, comprising:

• a light emitting element;
• and
• a light transmissive member having a light incident surface opposite to the light emitting element, and a generally planar light emitting surface,
• the light incident surface including an inner region having a retroreflective lens portion and directly facing the light emitting element and on an optical axis thereof, and an outer region having a shape different from a shape of the retroreflective lens portion, the inner region of the light incident surface having a circular planar shape continuously extending throughout the inner region, a diameter of the inner region being the same as or smaller than a maximum diameter or a maximum length of one side of an emission surface of the light emitting element,
• the retroreflective lens portion being configured to return light incident on a light emission surface, which is opposite from the light incident surface, back toward the light emission surface, and
• the outer region being a Fresnel lens portion including a plurality of unit Fresnel lens segments arranged in a circumferential direction, each of the unit Fresnel lens segments including a lens surface and a rise surface, the Fresnel lens portion including a plurality of convex vertex portions at each of which the lens surface of one of the unit Fresnel lens segments being linked to the rise surface of an adjacent one of the unit Fresnel lens segments, the convex vertex portions being arranged on a single plane extending parallel to the light emitting surface of the light transmissive member.