PoC server has an audio data receiving section 305 that receives the audio data transmitted from a cellular phone, an audio data transmitting section that transfers the audio data to individual cellular phones other than the speaker's one, of two or more cellular phones, a receiving user storage section that stores therein receiving association data indicative of the association between the cellular phone having the speaker right and the cellular phones of the receiving users, and a receiving user grasp section that causes the audio data transmitting section to transfer the audio data with designation of the cellular phone of the receiver.