A communication control method of controlling a communication flow by placing a module on a communication flow path for controlling the communication flow present through a network, the communication control method comprising: controlling or observation processing a signal of the communication flow by a communication signal control module placed in a communication device on the communication flow path, and then transmitting the processed signal; monitoring a state regarding the communication flow, based on requirement conditions about the communication flow provided by an application or an operator or automatically detected; composing a sequence of communication signal control modules in a communication control unit of said communication device for controlling the communication flow in order to meet the requirement conditions when the communication flow state does not meet the requirement conditions provided by the application or the operator, and a communication control adjustment module for placing or eliminating in said communication control unit a communication signal control module at a determined position in said sequence on the communication flow path; and downloading the communication signal control module and the communication control adjustment module through a communication terminal and a communication device from a server in the network in which those modules are stored, and activating the downloaded communication signal control module and communication control adjustment module to realize control of the communication flow and satisfy the requirement conditions; wherein the method further comprises: placing an application interface unit, a transmission frame processing unit, and a reception frame processing unit on the communication terminal; guaranteeing that no data exists in the communication signal control module between the application interface unit on the communication terminal on the transmission side and the transmission frame processing unit; guaranteeing that no data exists in the communication signal control module between the application interface unit on the communication terminal on the reception side and the reception frame processing unit; describing in a frame a chain number for identifying a set of communication signal control modules on the transmission side, by performing a frame assignment processing at the transmission frame processing unit; detecting a data boundary in which the set of the communication signal control modules on the transmission side has changed, by monitoring the chain number at the reception frame processing unit, to insert or eliminate the communication signal control modules on the reception side at the timing; and guaranteeing that communication data sent by a transmission application is transferred to a reception application in the same form to insert or eliminate the communication signal control module. controlling or observation processing a signal of the communication flow by a communication signal control module placed in a communication device on the communication flow path, and then transmitting the processed signal; monitoring a state regarding the communication flow, based on requirement conditions about the communication flow provided by an application or an operator or automatically detected; composing a sequence of communication signal control modules in a communication control unit of said communication device for controlling the communication flow in order to meet the requirement conditions when the communication flow state does not meet the requirement conditions provided by the application or the operator, and a communication control adjustment module for placing or eliminating in said communication control unit a communication signal control module at a determined position in said sequence on the communication flow path; and downloading the communication signal control module and the communication control adjustment module through a communication terminal and a communication device from a server in the network in which those modules are stored, and activating the downloaded communication signal control module and communication control adjustment module to realize control of the communication flow and satisfy the requirement conditions; placing an application interface unit, a transmission frame processing unit, and a reception frame processing unit on the communication terminal; guaranteeing that no data exists in the communication signal control module between the application interface unit on the communication terminal on the transmission side and the transmission frame processing unit; guaranteeing that no data exists in the communication signal control module between the application interface unit on the communication terminal on the reception side and the reception frame processing unit; describing in a frame a chain number for identifying a set of communication signal control modules on the transmission side, by performing a frame assignment processing at the transmission frame processing unit; detecting a data boundary in which the set of the communication signal control modules on the transmission side has changed, by monitoring the chain number at the reception frame processing unit, to insert or eliminate the communication signal control modules on the reception side at the timing; and guaranteeing that communication data sent by a transmission application is transferred to a reception application in the same form to insert or eliminate the communication signal control module.