Provided are an apparatus for continuous electrolytic treatment of a steel sheet that is suitable for producing a surface-treated steel sheet and a method for producing the surface-treated steel sheet using the apparatus for continuous electrolytic treatment of a steel sheet. The apparatus includes N pairs of tabular electrodes having a length L and being arranged to respectively face two surfaces of a steel sheet. Each electrode includes n sections arranged in the longitudinal direction of the electrode and disposed on the surface of the electrode facing the steel sheet surface. Each section is constituted by a conductive portion including an electrode portion having a length T1 and a nonconductive portion made by making an electrode portion having a length T2 nonconductive, where n×N≧10, 0.96≧T2/(T1+T2)≧0.05, and 0.9≧T1/L≧0.1.