Abstract: A light radiating device (1A) performs solidification or cauterization of a biological tissue (PL) by radiating a light beam (BM). A light source (10A) emits the light beam (BM). An optical waveguide (20A) is a member being provided with a reflection surface (21A) totally reflecting the light beam (BM) on an inner circumferential side wall, causing the light beam (BM) emitted from the light source (10A) to enter a part enclosed by the inner circumferential side wall from one end, and sending the light beam (BM) to the other end. A catoptric system (30A) reflects the light beam (BM) sent to the other end of the optical waveguide (20A) and condenses the light beam (BM) on the biological tissue (PL).