To enable a user to listen with the optimum stereo system with the number of speakers he has without being conscious by detecting the connection state of the speakers by an amplifier itself.

The speaker connecting circuit device is provided with a speaker driving means by which the speakers self-judge their connection or non- connection, a means for automatically changing the down mix method according to the number of connected speakers and the method of multichannel stereo sound to be reproduced, and an amplifying means for driving the speakers by performing the predetermined down mix according to the number of connected speakers and the method of multichannel stereo sound to be reproduced.