To control the volume level of a speaker on a fixed level all the times even if the sound mode of a television receiver is switched from monaural to stereo.

A sound recognizing device 11 being a sound pressure level detecting part communicating with a microphone 10 detects the sound pressure level of sound outputted from the speaker of a television receiver capable of receiving voice multiplexed broadcasting, and a controlling part 12 controls a volume adjusting device 7 so as to make the output of a speaker 9 a fixed sound pressure level. Also, the sound pressure difference between when the speaker output of the television receiver is monaural and when it is stereo is stored, the television receiver detects whether it is monaural broadcasting or stereo broadcasting, and the speaker output can be controlled to be constant even when sound modes are changed.