A communication apparatus includes a first connector, a communication unit, and at least one processor. The first connector is configured to be attachable to and removable from a second connector of a portable telephone to which a cable is attached in transmission and reception of data to and from another device. The communication unit is configured to convert data into a radio signal and transmit the radio signal and to convert a received radio signal into data. The processor is configured to receive data from a portable telephone through the first connector, output the received data to the communication unit, receive data converted by the communication unit, and output the received data to a portable telephone through the first connector.