In a communication apparatus, an encoder compresses telephone call voice which is transmitted from another communication apparatus. A voice accumulator preserves the telephone call voice, which is compressed by the encoder, as a message. A decoder expands the telephone call voice which is preserved in the voice accumulator. A signal memory temporarily maintains the telephone call voice which is expanded by the decoder. A speech speed convertor performs speech speed conversion on the telephone call voice, which is read from the signal memory, and outputs resulting voice from a speaker. A memory monitor temporarily stops to expand the telephone call voice in the decoder in a case where the memory monitor determines that an idle capacity of the signal memory approaches a predetermined lower limit value.