PURPOSE: To decrease a load of a processor executing signal processing, by providing two sound transmission buffers, and automatically writing an sound data of a CODEC encoding output section to a buffer, and alternately toggling the write and transmission of the sound data.

CONSTITUTION: A sound transmission buffer 22 of a sound transmission buffer packetting the sound at a CODED encoding section and transmitting the sound to a system bus 8 is provided with two sound storage areas 22a, 22b having the same capacity of the length of the information section of sound packet. The sound packet from a line 10 is gated with a unidirectional gate 23 of the buffer section to control a bidirectional gate 24. The output of the gate 24 switches a sound switching device 21 to control the gates 23 and 24 and the sound packet is writen in the buffer 22. The gate 23 switches a switch 26 to superimpose an output of an address generator 25 on a line 12, the areas 22a, 22b of the buffer 22 are designated at each prescribed bit and the writing and transmission to the bus 8 are alternately switched.