PURPOSE: To measure the call characteristic at each line easier than a conventional method, by incorporating a part of a test function to an exchange main body.

CONSTITUTION: A specific number is dialed from a telephone terminal 11 at first, with a terminal 14a of an MDF terminal board 14 connected with a digital exchange main body 15. Then, the number is connected to a test trunk 18 having plural test circuits incorporated in the exchange main body through a line via a digital switch unit 17 from a terminal interface unit 16. After the connection, a telephone terminal 11 is switched to a measuring device 12 with a switching device 13. Further, the call characteristic is tested between the measuring device 12 and the digital switch 17. Thus, the call characteristic per line is measured efficiently.