in a telephone switching system having a main - speech - path switch , connected to a plurality of subscribers and a plurality of board trunks , the connection in the main - speech - path switch is controlled as follows . in the first mode , the connection between a calling channel and one of the board trunks and the connection between a called channel and the board trunk are established through the main - path - switch , so as to selectively enable speech between an operator connected to said board trunk and one of a calling subscriber and a called subscriber . in the second mode , the connections between the calling channel and the called channel is directly established in the main - speech - path switch , while simultaneously connecting the two channels to the board trunk through the main - speech - path switch , so as to enable to monitor the speech between the calling subscriber and the called subscriber by the telephone operator . in the third mode , the main - speech - path switch effects only the connection between the calling channel and the called channel , while clearing the connection between said two channels and said board trunk . thus , the main - speech - path switch is free from the board trunk except for the monitoring and the initial connection operation , and can increase the exchange capability .