The present invention provides a nucleic acid detector for detecting a base sequences of a target DNA of interest, which comprises a DNA chip in which probe DNA and electrochemiluminescent material such as tris(2,2′-bipyridyl) metal complex, or derivatives thereof are immobilized on a surface of gold electrode; an electrochemical apparatus for applying a predetermined voltage to the DNA chip with respect to a reference electrode; and an optical measurement apparatus for measuring electrochemiluminescence generated from the DNA chip. The present invention also provides a method for producing the said detector for nucleic acids, and method for detecting nucleic acids using the same in a cost-saving way with high sensitivity.