PURPOSE:To diffuse light energy effectively and irradiate a chlorella with it discontinuously by connecting plural photoconductor rods lengthwise, providing a light scattering space room to each connection surface, and rotating the rods. CONSTITUTION:The photoconductor rods 21, 22, and 23 are stored in a transparent cylindrical body 5 while connected together lengthwise, light scattering space rooms 71 and 72 are provided to connection surface 61 and 62, and the cylindrical body 5 is rotated by a driving means 4. Light energy from a sunlight collecting device is converged by a lens and introduced into the rods 2 from the photoconductor cable 1; and the energy is reflected by wall surfaces of the light scattering space rooms and diffused and radiated out through the cylindrical body 5. The rods 2 are rotated by the driving means 4, so the light is radiated at specific intervals. Consequently, an irradiated body such as a chlorella is irradiated wth the diffused light effectively and discontinuously.