To provide a message communication method whereby a message is transmitted / received between a mobile phone 40 on a mobile phone communication network 10 and a LAN terminal on a LAN without the need for using a leased line causing a cost increase.

When the mobile phone 40 transmits a message to a particular personal computer 21A on the LAN 20, the mobile phone 40 transmits message data to a communication relaying apparatus 30 by designating the personal computer, and when the communication relaying apparatus 30 receives the message data from the mobile phone 40, the communication relaying apparatus 30 converts the communication protocol and transfers the message data to the personal computer. On the other hand, when the personal computer 21A on the LAN 20 transmits a message to the particular mobile phone 40, the personal computer 21A transmits the message data to the communication relaying apparatus 30 by designating the mobile phone 40, and when the communication relaying apparatus 30 receives the message data from the personal computer, the communication relaying apparatus 30 converts the communication protocol and transfers the message data to the mobile phone 40.