A vehicle-mounted millimeter-wave communication device mounted on a host vehicle for performing communication while temporally changing a communication direction by using an antenna unit capable of changing directivity, the communication device comprising: a detection unit configured to detect a direction of a communication partner present around the host vehicle, wherein the direction is given as a direction from the host vehicle to the communication partner; and a communication control unit (5, 52) configured to perform control such that a first longer communication time is set for the direction of the communication partner than for another direction, wherein the antenna unit can perform communication in only one angle range at a time; characterized by one of: the vehicle-mounted millimeter-wave communication device further comprises a communication type acquisition unit configured to acquire a type of a content of communication with the communication partner, and the communication control unit (5, 52) performs control that sets a second longer communication time for the direction of the communication partner in a case where the type of the content of the communication with the communication partner is related to control of a vehicle; and the vehicle-mounted millimeter-wave communication device further comprises a communication volume acquisition unit configured to acquire a volume of communication with the communication partner, and the communication control unit (5, 52) performs control that sets the second longer communication time for the direction of the communication partner in a case where the volume of the communication with the communication partner is not less than a threshold value, wherein the second longer communication time is longer than the first longer communication time. a detection unit configured to detect a direction of a communication partner present around the host vehicle, wherein the direction is given as a direction from the host vehicle to the communication partner; and a communication control unit (5, 52) configured to perform control such that a first longer communication time is set for the direction of the communication partner than for another direction, wherein the antenna unit can perform communication in only one angle range at a time; characterized by one of: the vehicle-mounted millimeter-wave communication device further comprises a communication type acquisition unit configured to acquire a type of a content of communication with the communication partner, and the communication control unit (5, 52) performs control that sets a second longer communication time for the direction of the communication partner in a case where the type of the content of the communication with the communication partner is related to control of a vehicle; and the vehicle-mounted millimeter-wave communication device further comprises a communication volume acquisition unit configured to acquire a volume of communication with the communication partner, and the communication control unit (5, 52) performs control that sets the second longer communication time for the direction of the communication partner in a case where the volume of the communication with the communication partner is not less than a threshold value, wherein the second longer communication time is longer than the first longer communication time. the vehicle-mounted millimeter-wave communication device further comprises a communication type acquisition unit configured to acquire a type of a content of communication with the communication partner, and the communication control unit (5, 52) performs control that sets a second longer communication time for the direction of the communication partner in a case where the type of the content of the communication with the communication partner is related to control of a vehicle; and the vehicle-mounted millimeter-wave communication device further comprises a communication volume acquisition unit configured to acquire a volume of communication with the communication partner, and the communication control unit (5, 52) performs control that sets the second longer communication time for the direction of the communication partner in a case where the volume of the communication with the communication partner is not less than a threshold value, wherein the second longer communication time is longer than the first longer communication time.