PURPOSE: To shorten the time required for antenna alignment in a mobile communication system utilizing a directive antenna by measuring the relationship between the strength of receiving field and the directivity of antenna at the time of adjusting the antenna alignment and determining the directivity of antenna based on the variation in the strength of receiving field and the variation pattern thereof.

CONSTITUTION: The beam direction of a directive antenna 1 is scanned at an antenna drive section 2, strength of receiving field is measured by a field strength measuring unit 5 and the strength of receiving field is recorded, along with the directivity of the antenna 1, at a data recording section 6 thus determining the directivity of the antenna 1 at an alignment control section 8.