A parabolic modulation circuit multiples a horizontal parabolic signal and a vertical modulation signal together, to amplitude-modulate the horizontal parabolic signal using the vertical modulation signal, and modulates the phase of the horizontal parabolic signal on the basis of the vertical modulation signal, to output the modulated horizontal parabolic signal to a correction current output amplifier. When an NS pincushion distortion on a screen of a CRT is asymmetrical, a horizontal parabolic signal generation circuit is so set as to generate an asymmetrical horizontal parabolic signal. A gull-wing distortion can be corrected by adjusting the value of n in an n-th power waveform generator in the horizontal parabolic signal generation circuit.