A waveform improving apparatus improves the contour of a waveform of a first signal which has a reduced frequency band by using a control signal generated from a second signal which has a correlation to the first signal. A waveform adjusting circuit increases the level of the first signal waveform at the rising slope portion thereof and decreases the level of the first signal waveform at the falling slope portion thereof to obtain a waveform-adjusted first signal. A control pulse generating circuit differentiates the second signal twice to obtain a control pulse having a predetermined duration and terminating at the center of a slope portion of the first signal waveform. A sample/hold circuit is responsive to the control pulse for sampling a level of the waveform-adjusted first signal and holding the sampled level during the duration of the control pulse thereby obtaining a waveform improved first signal.