PURPOSE: To attain the transfer of calls from a video telephone to a regular telephone.

CONSTITUTION: When a transfer request of a call from a video telephone set 3a to a general telephone set 5b in an extension telephone system place while a video telephone set 3b of a trunk line side and the extension video telephone set 3a are busy, a central control unit starts a video telephone signal processing unit 6 and controls an exchange switch 6 to connect the video telephone set 3b of a trunk line side and the extension video telephone set 3a to the video telephone signal processing unit 6. The video telephone signal processing unit 6 uses in-channel information to negotiate the communication capability with the video telephone set 3b of a trunk line side and converts voice information obtained from the general telephone set into compressed voice information for a video telephone set by using the information obtained in this way and sends the converted information to the video telephone set 3b and converts the compressed voice information obtained from the video telephone set into general telephone voice information and sends it to the general telephone set.