Abstract: An active noise control system cancels vibration and noise based on an output from an adaptive notch filter. When the difference between a current engine pulse value input to the adaptive notch filter and a past engine pulse value within a predetermined time period exceeds a predetermined level, an engine pulse monitor turns off a switch to stop the output from the adaptive notch filter. As a result, when there is a sudden change in the engine rpm, the output from the adaptive notch filter is stopped before the renewal speed of the adaptive notch filter coefficient becomes too fast to follow and the coefficient diverges, to prevent generation of abnormal sound. With this active noise control system, the user will not hear any abnormal sound from the adaptive notch filter even when there is a sudden change in the engine pulse.