Abstract: A communication apparatus for performing acoustic communication underwater includes a forward adaptive equalization circuit configured to perform waveform equalization on a data frame acquired by the acoustic communication in chronological order, a backward adaptive equalization circuit configured to perform waveform equalization on the data frame in reverse chronological order, and a selection synthesis circuit configured to sequentially select and output one of first data of a first equalizer output from the forward adaptive equalization circuit and second data of a second equalizer output from the backward adaptive equalization circuit, or to sequentially synthesize and output both of the first data and the second data.