PURPOSE: To send/receive plural voice signals through one B channel for the voice signal processing system that can be connected to an ISDN network.

CONSTITUTION: An exchange is provided with a compression enable subscriber number storage section 2, a line state storage section 3, a compression expansion device 7, a subscriber number collation section 5, a line state collation section 6 and a connection control section 4. When the connection control section 4 detects a voice call, the control section 4 makes a request of collation of a subscriber number sent from a caller to the subscriber number collation section 5 and obtains the result of subscriber collation representing it that the subscriber number is accommodated in the exchange in which voice compression and expansion are available, the control section 4 sends the result of subscriber collation to the line state collation section 6 to make collation request of a current line state. When its own station is in compression voice communication with an opposite exchange represented in the above result of subscriber collation at present and obtains the result of collation representing there is any unused part in the B-channel in operation, the unused part of the B-channel in operation is used and plural compressed voice signals are sent/received.