PURPOSE: To provide a measuring device which can easily, quickly, and accurately measure the dislocation amount of an electron beam in the deflection center in the adjusted state of color CRT purity.

CONSTITUTION: Normal horizontal deflecting current and normal vertical deflecting current are respectively allowed to flow into a pair of horizontal deflecting coils HL, HR and a pair of vertical deflecting coils VU, VL of a measuring deflecting coil for 3, and sine-wave current is allowed to flow so that respective magnetic fields in the deflecting center by means of the pair of horizontal deflecting coils HL, HR are canceled mutually. The sine-wave current is allowed to flow into the pair of vertical deflecting coils VU, VL so that respective magnetic fields in the deflecting center by means of the pair of vertical deflecting coils VU, VL are canceled mutually, and DC current, whose polarity and level change, is supplied to the horizontal correction coils C1, C2 of a measuring correction coil 4. The DC current, whose polarity and level change, is further supplied to the vertical correction coils C3, C4 so that the DC current, allowed to flow into the horizontal correction coils C1, C2, is detected, and the DC current, allowed to flow into the vertical correction coils C3, C4, is detected.