To obtain confocal effect which has no cross talk in all fluorescent rays and is most suitable to every detected fluorescent ray when plural fluorescent rays are detected.

On an outward way of a X galvanomirror 14a, laser wavelength 488 nm is selected and opening/closing control is executed to attain confocal pinhole radius of 105 μm which is the most suitable to the fluorescent ray by fluorescent pigment FITC. On way back, laser wavelength 633 nm is selected and opening/closing control is executed to attain confocal pinhole radius of 135 μm which is most suitable to the fluorescent ray by fluorescent pigment Cy5.