PURPOSE: To allow the device to listen to a sound in an optimum sound volume at all times without a troublesome sound volume change by comparing and collating the voice generated in itself with a surrounding voice sound and adjusting automatically the sound volume generated in itself in matching with the magnitude of the surrounding sound.

CONSTITUTION: A voice comparison collation means 4 extracts the collection result of a voice collection means 3 and a voice data stored in a voice storage means 2 and eliminate the voice generated in itself from the collected surround voice and calculates the resulting data as the surrounding noise sound and compares and collates whether or not the calculated value reaches the set sound volume revision. A sound volume adjustment means 5 applies sound volume adjustment processing based on the output result of voice comparison collation means 4. Thus, a troublesome sound volume revision is not required in matching with the surrounding environment and the sound is listened to in an optimum sound volume at all times.