PURPOSE: To measure the quality of line with only the operation from a control station side by sending a special number from a control station side measuring means to a terminal station so as to start a switching means of the terminal station side and using the switching circuit so as to form a loopback loop.

CONSTITUTION: The control station side equipment 1 sends a measured call code of a measurement object terminal station from a control section 14 to a line controller 3 to start the switching means. A terminal station side equipment 6 collates the measured call code to start the control section 15 of the changeover device 9 and to send the measurement call reply signal to the control station. The started control section 15 throws the contact of a changeover circuit 10 to the position of (a) and (b) to form a loopback loop. Upon the receipt of the measurement call reply signal from the terminal station side, the control section 14 of the measurement device 5 of the control station side throws the contact of a changeover circuit in to the position of (b) and (d) to send a test signal from a signal generator 11. The quality of line between the control station and the terminal station is measured by having only to apply operation from the control station side.