A method for providing echo cancellation between a first and second communication unit detects an echo condition between first and second communication units. The first phase-shift region and the second phase-shift region are alternately arranged and the third phase-shift regions are formed at the terminal ends of the first phase-shift region. The width of the overlap is set to a value satisfying a condition that an electric field induced between the signal line and pixel electrode will not invade into the pixel field defined with the black matrix.