PURPOSE: To attain voice warning notice of talking forced interruption due to shortage of charge.

CONSTITUTION: The exchange is provided with a channel 3 connecting a caller and a receiver telephone set 1, an externally mounted charge deposition device 6 by which a coin is deposited, a host computer calculating the remaining charge attended with talking with respect to the deposited coin, a central controller 4 connecting a voice synthesizer 7 to the channel 3 when it is informed in advance by the host computer 5 that the remaining charge approaches 0 and executing talking forced interruption to the channel 3 when it is informed that the remaining charge is 0, and the voice synthesizer 7 implementing voice warning notice of talking forced interruption due to shortage of charge to both talking parties in the connection to the channel 3.