[Objective] To emit light over a wide illumination area with a sufficient amount of light. [Constitution] An optical fiber (21) guides light output from a light source to an ultrasound probe (10). A light guiding plate (11) guides the light from a light input end, which is optically coupled with the optical fiber (21) to a light output end provided in the vicinity of ultrasonic transducers. The light guiding plate (11) has a first light guiding portion that includes the light input end, and a second light guiding portion that includes the light output end. The first light guiding portion is formed by glass, and magnifies input light. The second light guiding portion is formed by resin, and emits the light toward a subject from the light output end.
