A communication device mounted on a vehicle, comprising: reception means configured to receive a packet containing forwarding information that represents a transmission direction of the packet that is set up based on a reference direction from a transmission source; acquisition means configured to acquire a running direction of its own vehicle; control means; changing means; and transmission means configured to transmit the packet to at least the transmission direction of the packet that has been set up based on the running direction of said own vehicle, wherein said acquisition means is configured to acquire the position of its own vehicle, wherein said forwarding information further represents a transmission direction of said packet transmitted by the transmission source, an angle threshold to the transmission direction of said transmission source, and a position of said transmission source, wherein said control means is configured to acquire the forwarding direction of the packet forwarded from the position of said transmission source represented by said forwarding information to the position of said vehicle itself and prevents forwarding of said packet if the angle between the forwarding direction and the transmission direction of said transmission source represented by said forwarding information exceeds said angle threshold represented by said forwarding information, wherein said changing means is configured to change the reference direction of said transmission source represented by said forwarding information from the running direction of said transmission source to the running direction of its own vehicle and change the position of the transmission source represented by said forwarding information to the position of its own vehicle if said angle does not exceed said angle threshold, and wherein the transmission means is configured to transmit the packet containing the forwarding information that has been changed by said changing means to at least the transmission direction of the packet that has been set up based on the running direction of said vehicle itself. reception means configured to receive a packet containing forwarding information that represents a transmission direction of the packet that is set up based on a reference direction from a transmission source; acquisition means configured to acquire a running direction of its own vehicle; control means; changing means; and transmission means configured to transmit the packet to at least the transmission direction of the packet that has been set up based on the running direction of said own vehicle, wherein said acquisition means is configured to acquire the position of its own vehicle, wherein said forwarding information further represents a transmission direction of said packet transmitted by the transmission source, an angle threshold to the transmission direction of said transmission source, and a position of said transmission source, wherein said control means is configured to acquire the forwarding direction of the packet forwarded from the position of said transmission source represented by said forwarding information to the position of said vehicle itself and prevents forwarding of said packet if the angle between the forwarding direction and the transmission direction of said transmission source represented by said forwarding information exceeds said angle threshold represented by said forwarding information, wherein said changing means is configured to change the reference direction of said transmission source represented by said forwarding information from the running direction of said transmission source to the running direction of its own vehicle and change the position of the transmission source represented by said forwarding information to the position of its own vehicle if said angle does not exceed said angle threshold, and wherein the transmission means is configured to transmit the packet containing the forwarding information that has been changed by said changing means to at least the transmission direction of the packet that has been set up based on the running direction of said vehicle itself.