PURPOSE: To provide an FM equalizer device capable of demodulating high picture quality even when the ratio between the carrier and the lower sideband of an FM signal is different from each other due to the difference, etc., of tape quality (frequency characteristic).

CONSTITUTION: A cosine equalizer is constituted of delay lines 11, 12, adders 13, 16, an amplitude adjuster 14 and a phase inverter 15. This device is provided with a lower sideband detector 17 whose input end is connected to the other end of the delay line 11 and whose output end is connected to the control end of the amplitude adjuster 14. Then, by controlling the output of the amplitude adjuster 14 according to a lower sideband component detected by the lower sideband detector 17, the characteristic of the cosine equalizer is changed dynamically, and the lower sideband component with a suitable level is obtained.