PURPOSE: To obtain a selection control system of a balanced connection network which is capable of reducing a measuring time, by using a white noise without using a single frequency when appreciating one balanced connection network, and decreasing the number of times of measurement.

CONSTITUTION: When a signal is applied from a white noise generator, a white noise is added to a two-wire and four-wire converting circuit 3 through an encoder 12, a time division network 10 and a decoder 9, and in this case, depending on a degree of matching of impedance of a two-wire side subscriber's line connected to the two-wire and four-wire convertng circuit, and a balanced connection network, the signal turns round, and the signal which has turned round is transmitted to a level meter 13 through an encoder 8, the time division network 10 and a decoder 11. Accordingly, turn-round can be measured by measurement of only once without applying separate signal frequency many times, and the balanced connection network connected to the two-wire and fourwire converting circuit 3 can be appreciated.