A cordless phone apparatus which includes at least one or more slave devices and a master device, the master device being configured to transfer slave device transfer data including image data or music data, selected by a wireless IP terminal, to the slave devices, the wireless IP terminal being wirelessly connected to the master device through a wireless LAN, wherein the master device includes a slave device information transmitter configured to transmit slave device information to the wireless IP terminal, the slave device information including slave device identification information on each slave device which is registered in the master device, wherein the slave device information includes at least one of wallpaper data information, thumbnail data information, and ringtone memory information, which are played back in the slave device, and conversion format information which is at least one piece of information of use CODEC information, a slave device transfer data receiver configured to receive slave device transfer data including destination slave device information indicating slave device identification information on a destination slave device from the wireless IP terminal, and configured to store the slave device transfer data in a storage, a destination slave device determiner configured to determine a slave device which is a destination of the slave device transfer data, based on the destination slave device information, a slave device transfer data transmitter configured to transmit the slave device transfer data to all of the destination slave devices which are extracted by the destination slave device determiner, characterized by the cordless phone apparatus further comprising a slave device transfer data converter (124, 155) configured to convert the slave device transfer data into a data format which is available in the destination slave device, based on a data type of the slave device transfer data and the conversion format information of the destination slave device, and wherein the slave device transfer data transmitter is configured to transmit the slave device transfer data after conversion performed by the slave device transfer data converter (124, 155). a slave device information transmitter configured to transmit slave device information to the wireless IP terminal, the slave device information including slave device identification information on each slave device which is registered in the master device, wherein the slave device information includes at least one of wallpaper data information, thumbnail data information, and ringtone memory information, which are played back in the slave device, and conversion format information which is at least one piece of information of use CODEC information, a slave device transfer data receiver configured to receive slave device transfer data including destination slave device information indicating slave device identification information on a destination slave device from the wireless IP terminal, and configured to store the slave device transfer data in a storage, a destination slave device determiner configured to determine a slave device which is a destination of the slave device transfer data, based on the destination slave device information, a slave device transfer data transmitter configured to transmit the slave device transfer data to all of the destination slave devices which are extracted by the destination slave device determiner, characterized by the cordless phone apparatus further comprising a slave device transfer data converter (124, 155) configured to convert the slave device transfer data into a data format which is available in the destination slave device, based on a data type of the slave device transfer data and the conversion format information of the destination slave device, and wherein the slave device transfer data transmitter is configured to transmit the slave device transfer data after conversion performed by the slave device transfer data converter (124, 155).