When the signal level of a signal AOD, to which a cancellation signal CND of ACD is added, is larger than the signal level of ACD, a rate of change calculation part 173 calculates the maximum value (=1) as a rate of change parameter for showing that the degree of noise cancellation should be made highest. When the signal level of AOD, to which CND of ACD is added, is smaller than the signal level of ACD, the rate of change calculation part 173 calculates a change parameter rate to show that the larger the difference between both the signal levels are, the lower the degree of the noise cancellation becomes. A cancellation signal generation part 175 then generates CND and transmits it to an addition part 171 while taking the values of the change parameter rate into consideration. As a result, proper noise control can be easily performed.
