An active noise control device for use with a reference signal source generating a reference signal having a correlation with a noise in a compartment, the active noise control device comprising: a reference signal input terminal configured to have the reference signal input thereto, the reference signal having the correlation with the noise in the compartment; a cancel signal generation block including at least an adaptive filter having a filter coefficient, the cancel signal generation block configured to generate a cancel signal in accordance with the reference signal; an output terminal configured to output the cancel signal received from the cancel signal generation block; an error signal input terminal configured to have an error signal input thereto, the error signal corresponding to a residual sound generated in the compartment due to interference between the noise and a cancel sound generated from a cancel sound source in response to the cancel signal; a data filter configured to have the reference signal input thereto and to output a filtered reference signal obtained by correcting the reference signal with simulated acoustic transfer characteristic data that simulates an acoustic transfer characteristic of a signal transfer path of the cancel signal; a least mean square operation unit configured to update the filter coefficient of the adaptive filter by using the error signal, the filtered reference signal, and a step size parameter; a level detection unit configured to have the reference signal input thereto; and a control block configured to have a signal level input thereto, the signal level being detected by the level detection unit to determine the signal level, wherein the reference signal source is located outside the compartment, wherein the signal transfer path is a signal path from the cancel signal generation block to the least mean square operation unit, and wherein the control block decreases a level of the cancel signal if determining that the signal level of the reference signal is equal to or less than a predetermined value; characterized in that the control block is operable to: generate a level adjustment coefficient in accordance with the signal level; and adjust the level of the cancel signal by multiplying, by the level adjustment coefficient, at least one of the cancel signal output from the cancel signal generation block, the reference signal input to the cancel signal generation block, and the filter coefficient of the adaptive filter. a reference signal input terminal configured to have the reference signal input thereto, the reference signal having the correlation with the noise in the compartment; a cancel signal generation block including at least an adaptive filter having a filter coefficient, the cancel signal generation block configured to generate a cancel signal in accordance with the reference signal; an output terminal configured to output the cancel signal received from the cancel signal generation block; an error signal input terminal configured to have an error signal input thereto, the error signal corresponding to a residual sound generated in the compartment due to interference between the noise and a cancel sound generated from a cancel sound source in response to the cancel signal; a data filter configured to have the reference signal input thereto and to output a filtered reference signal obtained by correcting the reference signal with simulated acoustic transfer characteristic data that simulates an acoustic transfer characteristic of a signal transfer path of the cancel signal; a least mean square operation unit configured to update the filter coefficient of the adaptive filter by using the error signal, the filtered reference signal, and a step size parameter; a level detection unit configured to have the reference signal input thereto; and a control block configured to have a signal level input thereto, the signal level being detected by the level detection unit to determine the signal level, wherein the reference signal source is located outside the compartment, wherein the signal transfer path is a signal path from the cancel signal generation block to the least mean square operation unit, and wherein the control block decreases a level of the cancel signal if determining that the signal level of the reference signal is equal to or less than a predetermined value; characterized in that the control block is operable to: generate a level adjustment coefficient in accordance with the signal level; and adjust the level of the cancel signal by multiplying, by the level adjustment coefficient, at least one of the cancel signal output from the cancel signal generation block, the reference signal input to the cancel signal generation block, and the filter coefficient of the adaptive filter. generate a level adjustment coefficient in accordance with the signal level; and adjust the level of the cancel signal by multiplying, by the level adjustment coefficient, at least one of the cancel signal output from the cancel signal generation block, the reference signal input to the cancel signal generation block, and the filter coefficient of the adaptive filter.