A hybridization detecting unit which includes a reaction region in which hybridization takes place, a plurality of sites (e.g., the surface of electrodes) arranged in the reaction region to which is fixed a nucleic acid for detection, and means for sequentially moving by dielectrophoresis the target nucleic acid introduced into the reaction region according to the order of arrangement of the sites to which is fixed a nucleic acid for detection. A sensor chip provided with the hybridization detecting unit. The detecting unit compulsorily moves the target nucleic acid into the region where a probe nucleic acid for detection exists, thereby increasing the probability of hybridization taking place.