A protein detecting device, which comprises: (1) a detecting unit having a bonding section, which has properties for specifically bonding to a protein to be detected, a detecting section for detecting the bonding of the protein to be detected to the bonding section, the detecting section being made up of a polynucleotide double strand and a charge separating group, and an electrode section detecting the change in electrical conductivity of, or amount of transferred charge in, the polynucleotide double strand modified by the bond of the protein, (2) a standard electrode, (3) a reference electrode, (4) a container for housing the detecting unit, the standard electrode and the reference electrode, and containing a sample solutions comprising the protein to be detected, and (5) a measuring unit for measuring the protein based on a signal detected in the detecting unit.