the present invention relates to a relay device enabling efficient management of a voice message and a caller to wait for transmission of the voice message in a short time . the relay device is located at a boundary between an existing telephone network and an ip network , converts and relays a voice signal and an ip packet . the relay device comprises a receiving unit receiving voice source data into which a voice message is digitized , a packet processing unit converting the received voice source data into a voice source data packet as the ip packet , a storage unit storing the converted voice source data packets , and a transmitting unit transmitting , when transmitting a designated voice message to a designated destination , the voice source data packet corresponding to the designated voice message among the stored voice source data packets .