PURPOSE: To make adjustment of convergence while the calculational result given on a display is checked, by calculating the relative location difference between R, G, B on the screen of an image receiving tube from RGB switching timing signal of a TV signal generator and a location measuring signal output of sensor, and by displaying this result from calculation.

CONSTITUTION: To a control part 14 an RGB switching timing signal 15 is given from a TV signal generator 1, and it is judged which component location signal of R, G, B, location measuring signals 10W13 are. This control part 14 calculates dislocation of pattern location of the R and B components sensor by sensor 6W9 with the G component pattern location as reference. This result from calculation is emitted to a display 17 as dislocation amount signal 16 between R, G, B at each measuring point, and the display 17 displays the dislocation for each measuring point. Adjustment is made by moving a deflecting yoke 5 so that the dislocation of the display 17 minimizes.