Vehicle-mounted millimeter-wave communication device and communication method

A vehicle-mounted millimeter-wave communication device mounted on a vehicle and performing communication while temporally changing a communication direction by using an antenna unit capable of changing directivity,

• the device comprising:
• an acquisition unit configured to acquire a relay request that requests relay of communication from a first communication partner;
• a detection unit configured to detect directions of the first communication partner and a second communication partner that are viewed from the vehicle;
• and
• a communication control unit configured to perform control such that, in a case where the relay request is received from the first communication partner and it is possible to communicate with the second communication partner, communication, in which a communication time longer than a communication time set for another direction is set for each of the directions of the first communication partner and the second communication partner, is performed, and communication between the first communication partner and the second communication partner is relayed.