A communication device (11;12;21;22;31;32;33;41;42;50), wherein the communication device (11;12;21;22;31;32;33;41;42;50) is connected to an external device (61;62;63) and configured to obtain external information from the external device (61;62;63), and the communication device (11;12;21;22;31;32;33;41;42;50) is connected to a communication line (10;20;30;40) and configured to perform information communication through the communication line (10;20;30;40) based on communication data specified by a CAN protocol, the communication device (11;12;21;22;31;32;33;41;42;50) comprising: a communication necessity determination unit (113;52) that is configured to determine whether or not the information communication through the communication line (10;20;30;40) is required based on the external information obtained from the external device (61;62;63), wherein the communication necessity determination unit (113; 52) is configured to determine that the information communication is not required when determining from the external information that an electronic computing unit, ECU, can solely process the external device (61;62;63); and a communication control unit (114;53) that is configured to stop the information communication during a fixed period, under the condition that the determination by the communication necessity determination unit (113;52) of whether or not the information communication is required is "affirmative" and that a communication error has been detected, and restart the information communication after the fixed period elapses, wherein the communication control unit (114;53) is configured to stop transmitting communication data, under the condition that the determination by the communication necessity determination unit (113;52) of whether or not the information communication is required is "negative" and that a communication error has been detected, until a predetermined transmission restarting condition is satisfied. a communication necessity determination unit (113;52) that is configured to determine whether or not the information communication through the communication line (10;20;30;40) is required based on the external information obtained from the external device (61;62;63), wherein the communication necessity determination unit (113; 52) is configured to determine that the information communication is not required when determining from the external information that an electronic computing unit, ECU, can solely process the external device (61;62;63); and a communication control unit (114;53) that is configured to stop the information communication during a fixed period, under the condition that the determination by the communication necessity determination unit (113;52) of whether or not the information communication is required is "affirmative" and that a communication error has been detected, and restart the information communication after the fixed period elapses, wherein the communication control unit (114;53) is configured to stop transmitting communication data, under the condition that the determination by the communication necessity determination unit (113;52) of whether or not the information communication is required is "negative" and that a communication error has been detected, until a predetermined transmission restarting condition is satisfied.