PURPOSE: To correct the trapezoidal distortion of a cathode ray tube by continuously changing a secondary side inductance with the flow of a saw tooth current to the primary side of a trapezoidal distortion correcting transformer.

CONSTITUTION: When the vertical deflecting saw tooth current flows to a vertical deflecting yoke LV1, a saw tooth voltage is generated at a junction between the negative terminal of the yoke LV1 and resistors R3 and R4. This voltage is divided by resistors R5-R7, inputted to the positive terminal of an operational amplifier IC1 while cutting the DC component by a capacitor C4, divided by the resistors R3 and R4 and inputted to the negative terminal while cutting the DC component by a capacitor C5, and the operational amplifier IC1 amplifies difference between the positive terminal and the negative terminal. The output voltage of the operational amplifier IC1 is inputted to the primary side of a trapezoidal distortion correcting transformer T3, and the secondary side inductance of the transformer T3 is changed by the current flowing through the primary side. As a result, the trapezoidal distortion is corrected by gradually increasing or decreasing the horizontal deflecting current from the upside to the downside of a picture.