A call recording system configured to transmit, over an IP network, call audio data from an IP phone or another IP phone engaging in a voice call to a recording server as recording data so that the call audio data is recorded in the recording server, a call session for a voice call is held between the IP phone and the other IP phone of a conversing party, wherein in order to establish a recording session between the IP phone and the recording server for recording the call audio data, the IP phone is configured to transmit to the recording server a recording session establishing request that includes at least phone information for identifying the IP phone and the other IP phone, the recording server that has received the recording session establishing request from the IP phone is configured to check whether the recording session establishing request has already been received from the other IP phone by referring to the phone information for identifying the other IP phone included in the recording session establishing request, if the recording session establishing request has not been received from the other IP phone, the recording server is configured to establish a recording session with the IP phone transmitting the recording session establishing request and store the call audio data transmitted from the IP phone as the recording data thereafter, if the recording session establishing request has already been received from the other IP phone, the recording server is configured to refuse the received recording session establishing request and refrain from establishing a recording session with the IP phone that is the transmitter, wherein the IP phone is configured to upon receiving, from the recording server with which the recording session is being established, reception quality information transmitted as appropriate as information indicating a reception quality of the recording data transmitted by the IP phone, store the reception quality information as information on a quality of communication between the IP phone and the recording server and transmit the reception quality information to the other IP phone, if information on the quality of communication between the other IP phone and the recording server has been received from the other IP phone, compare the quality of communication between the IP phone and the recording server with the quality of communication between the other IP phone and the recording server, if the quality of communication of the IP phone is higher than the quality of communication of the other IP phone, continue with an operation of transmitting the call audio data to the recording server as the recording data, and if the quality of communication of the IP phone is lower than the quality of communication of the other IP phone, stop an operation of transmitting the call audio data to the recording server, and the recording data is the call audio data transmitted / received in the call session. in order to establish a recording session between the IP phone and the recording server for recording the call audio data, the IP phone is configured to transmit to the recording server a recording session establishing request that includes at least phone information for identifying the IP phone and the other IP phone, the recording server that has received the recording session establishing request from the IP phone is configured to check whether the recording session establishing request has already been received from the other IP phone by referring to the phone information for identifying the other IP phone included in the recording session establishing request, if the recording session establishing request has not been received from the other IP phone, the recording server is configured to establish a recording session with the IP phone transmitting the recording session establishing request and store the call audio data transmitted from the IP phone as the recording data thereafter, if the recording session establishing request has already been received from the other IP phone, the recording server is configured to refuse the received recording session establishing request and refrain from establishing a recording session with the IP phone that is the transmitter, wherein the IP phone is configured to upon receiving, from the recording server with which the recording session is being established, reception quality information transmitted as appropriate as information indicating a reception quality of the recording data transmitted by the IP phone, store the reception quality information as information on a quality of communication between the IP phone and the recording server and transmit the reception quality information to the other IP phone, if information on the quality of communication between the other IP phone and the recording server has been received from the other IP phone, compare the quality of communication between the IP phone and the recording server with the quality of communication between the other IP phone and the recording server, if the quality of communication of the IP phone is higher than the quality of communication of the other IP phone, continue with an operation of transmitting the call audio data to the recording server as the recording data, and if the quality of communication of the IP phone is lower than the quality of communication of the other IP phone, stop an operation of transmitting the call audio data to the recording server, and the recording data is the call audio data transmitted / received in the call session.