PURPOSE: To enable the distance between the inner surface of a panel and a shadow mask to be measured with a measurement device without causing it to touch the shadow mask, with a high measurement efficiency even when the shadow mask has a small plate thickness, and enable the measurement device to be used for a shadow- mask-type color picture tube having a small q value.

CONSTITUTION: High-frequency magnetic field oscillators 14 are provided on the inner surface of a panel 11 and buried in the holes of a flexible insulating base plate 13 made of an FRF plate or the like which are provided in the center and, for example, corner sections of the base plate 13. When a metallic plate approaches the oscillators 14 after they are oscillated by a high-frequency magnetic field, the oscillators 14 produce eddy currents, the intensity of which change almost linearly. Signals sent from the oscillators 14 are displayed on a display unit 22 which is the measurement-reading mechanism of a control board 21. When a shadow mask 16 is attached to a panel pin 18 through a supporting structure 17, eddy currents changing linearly according to the distances between the oscillators 14 and the shadow mask 16, develop. Therefore, by calculating a signal corresponding to each eddy current into a voltage which is then indicated on a display unit 22, whether q value is correct or not is judged.