A reaction container, a light source unit including light emitting devices that are different in wavelength of an emitted light beam and output dichroic mirrors that are different in wavelength range of a reflectible light beam, and a photoreceptive unit including photoreceptors and photoreceptive dichroic mirrors that are different in wavelength range of a reflectible light beam are used. The light emitting devices are arranged so that output directions thereof may be in parallel, and the output dichroic mirrors are arranged so that the reflected light beams may pass through the same optical path in the same direction. The photoreceptors are arranged so that photoreceptive surfaces may be in parallel, and the photoreceptive dichroic mirrors are arranged so that output light beams from the reaction container may be reflected by the photoreceptive dichroic mirrors and may enter the photoreceptors, according to wavelengths of the output light beams.