To enable a light-blocking practically sufficient to prevent a crosstalk, and at the same time prevent a cross contamination by a shading pipe part.

A photodetector 1 is allowed to correspond to a sample in a well 10a to be measured. In this case, distance B from the tip of a shading pipe part 2a to the upper wall surface of a micro plate 10 is set shorter than a thickness A of a wall that is a boundary for the adjacent well 10a, and it is preferably equal to or less than the half of the thickness A(B<A/2). Then, the shutter of a light reception part 1a is released only for a specific amount of time, and only weak luminescence from the sample in the to-be-measured well 10a immediately below is measured. In this case, light in an oblique lower direction produced from the adjacent well 10a or from a sample in another well 10a is reflected in an oblique upper direction by the outer-periphery surface of the shading pipe part 2a, and cannot reach the light reception part 1a as stray light.