PURPOSE: To perform all service charge controls through a single service charge controller, by using a dial reading unit and an interface unit provided within a service charge controller as well as an interface unit provided within the main device of a key telephone device.

CONSTITUTION: When a trunk line is connected to a single telephone set TS, a dial reading unit 2 within a service charge controller 1 receives the data on on- hook, dial, polarity inversion of the trunk line, off-hook, etc. from the set TS to perform the charge calculation. When the trunk line is connected to a key telephone set TB, an interface unit 4 provided in the controller 1 receives the telephone number sent from an interface unit 3 within a main device ME of a key telephone device through an interface cable W and the information on the dial data, etc. Thus the charge is calculated for each telepone set TB of an electronic key telephone device.