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 voice call is held between the IP phone and the other IP phone of a conversing party, wherein the IP phone that has established a recording session for recording the call audio data in the recording server transmits, to the recording server, data that includes at least the call audio data and phone information for identifying the IP phone and the other IP phone as the recording data, upon receiving the recording data from the IP phone, the recording server checks the phone information included in the recording data and checks whether the recording data is already stored, in the recording data, the information that identifies the IP phone that transmits the transmitted call data is the other IP phone, and the information that identifies the IP phone that receives the received data is the IP phone, if the recording data is not stored, the recording server stores the recording data received from the IP phone, and if the recording data is already stored, the recording server associates the phone information included in the recording data received from the IP phone with the stored recording data and discards the recording data received from the IP phone, 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 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. the IP phone that has established a recording session for recording the call audio data in the recording server transmits, to the recording server, data that includes at least the call audio data and phone information for identifying the IP phone and the other IP phone as the recording data, upon receiving the recording data from the IP phone, the recording server checks the phone information included in the recording data and checks whether the recording data is already stored, in the recording data, the information that identifies the IP phone that transmits the transmitted call data is the other IP phone, and the information that identifies the IP phone that receives the received data is the IP phone, if the recording data is not stored, the recording server stores the recording data received from the IP phone, and if the recording data is already stored, the recording server associates the phone information included in the recording data received from the IP phone with the stored recording data and discards the recording data received from the IP phone, 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 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.