The position of a mobile station is properly monitored and is stored in a home location register. A call which indicates this mobile station as a calling/receiving station is set via any mobile service switching center. When monitoring a communication oriented by this call is necessary, the subscriber number of this mobile station is input by a test work station. Based on this subscriber number, an operation and maintenance center reads position data of the mobile station from the home location register and reports the data to the test work station. Based on the position data, the test work station specifies the mobile service switching center through which the call has been set, and transfer data specifying this mobile service switching center to the operation and maintenance center. The operation and maintenance center extracts the call-oriented voices from this mobile service switching center.