A communication apparatus including: a communication portion which performs a data communication with a sub-communication apparatus; a transmission-data communicating portion which performs a transmission-data communication with a data processing apparatus; a transmission-data receiving section which receives transmission data from the data processing apparatus; a notifying section which transmits a notification to the sub-communication apparatus, the notification being based on that the transmission-data receiving section has received the transmission data; a relaying section which relays a phone conversation between an external communication apparatus and the sub-communication apparatus; and a transmitting section which transmits the transmission data received by the transmission-data receiving section, to an external communication apparatus as a call opposite party of the phone conversation which is being relayed by the relaying section where a transmission-data transmitting command has been received from the sub-communication apparatus performing the phone conversation being relayed by the relaying section.