To provide a luminaire capable of emitting uniform illuminating light.

This luminaire has a light source and a light guiding body. The light guiding body has a first side face to receive light from the light source, a second side face facing the first side face, a light emitting face almost perpendicular to the first side face, and a confronting face facing the light emitting face. The confronting face of the light guiding body is provided along a first direction perpendicular to the first side face in a prescribed period, and has a plurality of grooves extending in a second direction crossing the first direction. Each groove is composed of a plurality of faces, and the face closest to the first side face is an inclined face inclined relative to the first direction. An angle α made by the inclined face to the first direction, the refractive index n of the light guiding body, the thickness T of the light guiding body along the direction of the normal line of the light emitting face, the length L of the light guiding body along the first direction, the depth h of a plurality of grooves and the period p of a plurality of grooves satisfy n sin{90-α-tan-1(2 T/L)}≥1 and 2T/L≤h/p≤tan α.