To easily perform the handling and alignment of an optical fiber in an immunoassay device.

The end part on the side of the laser beam emitting end surface 4a arranged on the side of a specimen 10 of an exciting light incident optical fiber 4 and the end part on the side of the fluorescence incident end surface 5a arranged on the side of the specimen 10 of a fluorescence-measuring optical fiber 5 are fixed to a support 6. The support 6, to which the end parts of the exciting light incident optical fiber 4 and the fluorescence measuring optical fiber 5 are fixed, is moved toward the side of the side of the specimen 10 at measurement, and a laser beam is allowed to be incident to detect the fluorescence emitted from a fluorescence label 15. Since the exciting light incident optical fiber 4 and the fluorescence-measuring optical fiber 5 are fixed to the support 6, handling of the optical fibers is facilitated, the alignment of both fibers can be performed simply and the measurement due to the immunoassay device can be made efficient.