PURPOSE: To attain the work by advance wiring work through the use of an embedded box by constituting a unit main body by a body and a cover, incorporating the speaker into the body, using a mount frame and mounting the body to the embedded box.

CONSTITUTION: The unit main body 9 is constituted by the cover 7 and the body 8, a circuit board 11 is provided in the body 8, a cylindrical rib linked to a voice sounding hole 26 is projected to the rear face of the cover 7 and the speaker 15 is arranged. Then the outer size of the unit main body 9 is set to be mounted to the mount frame 29 of the ready-made wiring fixture, mount means 31, 32 to the mount frame 29 are provided to the unit main body 9, and it is mounted to the embedded box by using the mount frame 29. Thus, the advance wiring utilizing the ready-made mount frame is attained.