PURPOSE: To attain the measuring easily in a short time, by visualizing an irradiated output measuring area with a signal pattern for luminance measurement and reading the irradiated area.

CONSTITUTION: After a cathode-ray tube 1 to be measured is fitted, the operation of a deflecting system output adjusting device 22 is started and each power supply to operate the cathode-ray tube 1 is turned on. The irradiated area is adjusted into a prescribed size with an irradiated area reader 21 and a deflection system output adjusting device 22. A luminance signal is outputted from a signal generator 20 and applied to the cathode-ray tube 1 so that only the part measuring the irradiated output is measured. The irradiated output of the cathode-ray tube 1 is read at a luminance measuring device 9.