PROBLEM TO BE SOLVED: To provide a muffled sound reduction device or the like capable of sufficiently reducing muffled sound within an external auditory meatus that causes discomfort for a user while preventing oscillation that becomes a problem when performing negative feedback using a microphone for external auditory meatus.SOLUTION: The muffled sound reduction device comprises a receiver 4, a microphone 5 for external auditory meatus, signal estimation parts 42, 43 and 44, a subtraction part 45 and negative feedback parts 40 and 41. A signal S(n) is converted into sound by the receiver 4, and the sound is converted into a signal S(n) by the microphone 5 for external auditory meatus together with muffled sound. The signal estimation parts adaptively estimate transfer functions R(z), F(z) and M(z) for a predetermined frequency component, inputs the signal Sand generates an estimate signal y(n). A signal S(n)=S(n)-y(n) generated via the subtraction part 45 is negatively fed back by the negative feedback parts, thereby sufficiently reducing a frequency component of muffled sound while preventing the predetermined frequency component from being oscillated by a negative feedback loop.
