PURPOSE: To improve economy more by making a telephone call most cheaply in consideration of the speech time.

CONSTITUTION: At a request for origination which is made by an extension terminal TEL, the LCR origination control means 51a in the private branch exchange EX selects the cheapest carrier. Once a channel is formed through this carrier, a speech time information control means 51b sends the time for which a telephone call can be made at the lowest charge by using the carrier to the originationsource extension telephone set TEL, and the time is displayed on its LCD display unit. This displayed speech time is subtracted from by the extension TEL in the speech period and momentarily varies as the remaining speech time.