1. A method for removing a pseudo signal from an original signal which includes a main signal free from a zero-shift component and the pseudo signal consisting of zero-shift components, the method comprising the steps of: means for integrating said original signal with respect to time; means for decomposing said integrated original signal into the sum of one Approximation (A(t)) and at least one Detail (D(t)) by wavelet transformation with a level number deepened until which level number reaches to a threshold level number where the ratio of the energy of said one Approximation to the energy of said original signal has a predetermined relationship to a predetermined threshold value; means for setting said Approximation to zero at said threshold level number as a pseudo signal component by a threshold operation; means for deriving an integrated main signal by reconstituting said Details up to said threshold level and said Approximation previously set to zero by wavelet inverse transformation; and means for deriving said main signal by differentiating said integrated main signal with respect to time.