This paper proposes a method for dereverberating the power envelope from the reverberant signal. This method is based on the modulation transfer function (MTF) and does not require that the impulse response of an environment be measured. It improves upon the basic model proposed by Hirobayashi et al. regarding the following problems: (i) how to precisely extract the power envelope from the observed signal; (ii) how to determine the parameters of the impulse response of the room; and (iii) a lack of consideration as to whether the MTF concept can be applied to a more realistic signal. We have shown that the proposed method can accurately dereverberate the power envelope from the reverberant signal.