PURPOSE: To provide a demodulation device which is impervious to the influence of inter-code interference and noise owing to the shift of an initial phase and transmission distortion.

CONSTITUTION: A means 23 estimating all signals Xa(n), Xb(n), Xc(n) and Xd(n) which can be obtained this time based on previous reception data X(n-1), a means 24 calculating distances d(a), d(b), d(c) and d(d) between the signals Xa(n), Xb(n), Xc(n) and Xd(n) which are estimated in the estimation means 23 and the reception signal X(n) of this time and a means detecting the estimation signal of the shortest distance among the distances d(a), d(b), d(c) and d(d) which are calculated in the calculation means 24 and demodulating the reception signal based on the detected estimation signal are provided.