A signal processor for multiple gradations for carrying out coding by replacing an input image signal with a plurality of subfields, comprising a main path for generating a primary color signal having a first number of gradations, a sub-path for generating a primary color signal having a second number of gradations, which is smaller than the first number of gradations, a switch, a movement detection circuit, a level detection circuit, a path switching control circuit for switching the switch based on the amount of movement and the level, plural subfield coding circuits for carrying out subfield coding different from each another, a superposing circuit for selecting one of the outputs of the plural subfield coding circuits, and a superposing control circuit, and thus preventing a moving false contour.