A device for measuring convergence of color cathode ray tube including means for producing a white measurement pattern on a viewing screen of the color cathode ray tube, a color image pickup device for picking up the white measurement pattern on the viewing screen, a memory unit for storing color signals transmitted from the color image pickup device, a discrimination unit for discriminating which of blue, green, and red phosphors glows every picture elements of the color image pickup device based on signals from adjacent picture elements, and a calculation unit for a finding out a misconvergence from discriminated results assures an accurate convergence measurement by one time of image pickup only.