PURPOSE: To know a callable time from the beginning of call by a caller and to adjust the progress of a smooth call by providing an accounting index table classified by distance, a callable time calculating part, a selecting signal storing part, etc.

CONSTITUTION: An accounting index table 12 classified by the distance determines the accounting index classified by the distance from the exchange to which the public telephone set belongs until the opponent exchange, and the accounting index classified by the distance to arrange the area code is accommodated. A callable time calculating part 13 retrieves the area code part corresponding to the selecting signal stored at a selecting signal storing part 14 from the table 12. Next, the accounting index corresponding to the area code, the unit charge magnification value of the input amount and the remaining number of the magnetic card, the callable time is calculated. When the call is started, a subtracting part 16 starts the action by a control circuit 17, the callable time is subtracted for the unit time calculated by a timer 15 and displayed at the displaying part. Thus, the caller can know the callable time from the beginnig of the call and can adjust the smooth call process.