PURPOSE: To improve linearity of descrambled image and eliminate residual distortion by approximating sine wave for distortion correcting descrambling that approximates to ideal characterstic further to ideal characteristic by twofold sine wave signal generated by an oscillator that makes the sine wave trigger input.

CONSTITUTION: Base band scramble VIDEO is inputted to the multiplier 9 of a descrambling circuit and 15KHz (fH) sine wave for descrambling is inputted to a distortion correcting circuit 8 and a 2fH oscillator 20. Distortion correcting 15kHz sine wave that approximates to ideal characteristic is inputted from the distortion correcting circuit 8 to the multiplier 9. The oscillator 20 is triggered by 15kHz sine wave to generate 31kHz (2fH) sine wave, and level and phase are adjusted by a level and phase adjuster 21 to approximate to ideal waveform, and inputted to the multiplier 9. Distortion correction of ideal characteristic is made using 15kHz since wave and 31kHz sine wave, and thus, linearity of descrambled VIDEO is improved, and residual distortion of descrambling is eliminated.