To provide a noise removal method capable of removing effectively external noise other than a leakage sound regardless of a working time or a place, when performing leak detection.

The leakage sound by a vibration sensor 1 installed on the ground or the wall surface, a signal wherein the external noise is mixed, and a signal mainly composed of the external noise by a microphone 2 installed on a proper position on the ground are subjected respectively to fast Fourier transform, to thereby convert them into signals S1, S2 comprising frequency components. The signals S1, S2 comprising each frequency component are subjected to operation processing, to thereby generate a composite signal S3 wherein an external noise component is attenuated. The composite signal S3 is subjected to fast inverse Fourier transform, to thereby convert it into an output signal wherein the external noise is removed.

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