To provide the subject apparatus of a small volume having no head space and free from the occurrence of vaporizing and condensing of a reagent, etc., storing a liquid sample in the apparatus by suctioning it into a capillary section between a sample well and an optical window member and tightly closing it with a closing body.

Into a capillary section 54 between the upper surface of the bottom wall of a sample well 14 and an optical window member 20, a liquid sample 60 is introduced through a gap 58 with a pipette 66, etc., to be suctioned and the sample is tightly closed by covering with a closing body 18. A reagent in a spot 56, i.e., a dried reagent, which is to be used for homogeneous amplification and fluorescence polarization assay of nucleic acid and adhered on the central position of the upper surface of the bottom wall of the sample well 14, is hydrated to start the objective amplification and assay reactions.