A roadside communication apparatus configured to be mounted on a base station and to perform a wireless communication with a communication device being mounted on a mobile station, comprising: - an inter-vehicle transmission-and-reception service processing unit configured to transmit and receive a roadside-to-vehicle message based on a protocol of a roadside-to-vehicle communication and an inter-vehicle message based on a protocol of an inter-vehicle communication to and from the communication device; - a communication transfer unit configured to provide a transaction service including a retransmission and division-and-assembling of the roadside-to-vehicle message being transmitted to and received from the communication device via the inter-vehicle transmission-and-reception service processing unit and a transfer service adding a local port number for identifying an upper protocol; - a roadside-to-vehicle application processing unit configured to transmit and receive the roadside-to-vehicle message to and from the communication device via the inter-vehicle transmission-and-reception service processing unit and the communication transfer unit; - an inter-vehicle application processing unit configured to transmit and receive an inter-vehicle message to and from the communication device via the inter-vehicle transmission-and-reception service processing unit; - a transmission-and-reception condition management unit configured to manage a reception condition of the inter-vehicle message which the inter-vehicle application processing unit receives from the communication device; and - a roadside communication management unit configured to manage a connection state with the communication device, wherein the roadside communication management unit is further configured to manage a connection state with the communication device based on a reception condition of the inter-vehicle message notified by the transmission-and-reception condition management unit. - an inter-vehicle transmission-and-reception service processing unit configured to transmit and receive a roadside-to-vehicle message based on a protocol of a roadside-to-vehicle communication and an inter-vehicle message based on a protocol of an inter-vehicle communication to and from the communication device; - a communication transfer unit configured to provide a transaction service including a retransmission and division-and-assembling of the roadside-to-vehicle message being transmitted to and received from the communication device via the inter-vehicle transmission-and-reception service processing unit and a transfer service adding a local port number for identifying an upper protocol; - a roadside-to-vehicle application processing unit configured to transmit and receive the roadside-to-vehicle message to and from the communication device via the inter-vehicle transmission-and-reception service processing unit and the communication transfer unit; - an inter-vehicle application processing unit configured to transmit and receive an inter-vehicle message to and from the communication device via the inter-vehicle transmission-and-reception service processing unit; - a transmission-and-reception condition management unit configured to manage a reception condition of the inter-vehicle message which the inter-vehicle application processing unit receives from the communication device; and - a roadside communication management unit configured to manage a connection state with the communication device, wherein the roadside communication management unit is further configured to manage a connection state with the communication device based on a reception condition of the inter-vehicle message notified by the transmission-and-reception condition management unit.