Provided are an antenna angle adjustment device, an antenna angle adjustment system, an antenna angle adjustment method, and a communications device, whereby the angle of an antenna can be adjusted to a direction in which direct waves can be more reliably received. A direction information generation unit 41 generates direction information indicating a direction of one antenna from another antenna. A range information generation unit 42 generates range information indicating a range of a main beam of the another antenna. A determination unit 43 determines, based on the range information and the direction information, whether or not the one antenna is in a range indicated by the range information.