PURPOSE: To reduce thicked white dots by changing a detection output fed to a scanning speed modulation deflection means for a horizontal period so that the scanning speed modulation effect is reduced from a center of a screen toward the surrounding part.

CONSTITUTION: A horizontal amplitude modulation section 46 applies amplitude modulation to a signal differentiating an input video signal with a differentiation amplifier section 41, a waveform shape section 43 and a differentiation amplifier section 45 based on a horizontal synchronizing signal SH from a terminal 42. A vertical amplitude modulation section 48 applies amplitude modulation to a signal differentiating the input video signal with the differentiation amplifier section 41, the waveform shape section 43 and the differentiation amplifier section 45 based on a vertical synchronizing signal SV. The differentiation signal amplitude-modulated based on the signals SH, SV is amplified by an amplifier output section 47 and the result is fed to a speed modulation coil 5 of a picture tube 3. The differentiation current around the screen is reduced by applying amplitude modulation to the differentiation current flowing to the coil 5 by the horizontal synchronizing signal SH and the vertical synchronizing signal SV and the thicked white dot width around the screen is improved and the sharpness of the screen is improved.