We have investigated the surface potential change accompanying the variation in diamond surface chemisorbed structures using scanning Maxwell-stress microscopy. The hydrogen chemisorbed diamond surface was prepared by a hydrogen plasma treatment following the homoepitaxial (001) diamond growth by the microwave plasma-assisted chemical vapor deposition (MPCVD). The surface chemisorbed structure was controlled by increasing the oxidized temperature in the range from 100 degrees C to 500 degrees C. The hydrogen chemisorbed diamond surface showed a minimum work function value of 4.8 eV. A thermal oxidation of the hydrogen chemisorbed diamond surface at 500 degrees C yielded the oxygen chemisorbed diamond surface, which showed a maximum work function value of 5.8 eV. The surface potential value, which corresponds to the surface work function value, was strongly influenced by the species of the chemisorption on the diamond surface.