The present invention has the object to decrease the peak factor of a transmission signal and control impulse noise. The amplitude characteristics are identical to those of a normal root Nyquist filter, and the phase characteristics divide the passband into a plurality number, the root Nyquist filters having the phase corresponding to each bit value of PN codes with the length of the divided number are set on transmission and reception. Accordingly, even when the transmission signal has a high amplitude peak and a short connection time, the signal can be transmitted along the route by decreasing the peak to control the peak factor. Also, impulse noise can be restrained at reception.