PURPOSE: To automatically adjust the incoming sound volume of a telephone set in accordance with an environmental condition.

CONSTITUTION: A brightness and darkness identification part 2 detects the degree of the brightness/darkness surrounding the installed telephone set at the time of incoming to the telephone set, compares the detected brightness and a previously-set brightness reference value and outputs the result. A sound control part 3 controls a current to be impressed to a speaker 4 in accordance with the result outputted by the brightness identification part 2.