An adaptive digital filter (10) is adapted to generate a pseudo echo Se
which is produced by imitating a noise, using part of receiving signals Si and
to output it. An echo produced through an echo path (15) is mixed, as an
echo noise, with a sending signal So and this sending signal is attenuated by a
level attenuator (6). The level attenuator (6), in order to match
the amplitude level of the echo noise of the sending signal So to that of the pseudo
echo, attenuates the sending signal So and feeds it to a subtracter (7).
The subtracter (7) eliminates echo noises by subtracting the pseudo echo
Se from the sending signal So. Even if the echo path is in the state of amplified
system, the complete elimination of the echo can be achieved accordingly.
