To obtain an array antenna capable of reducing increase in side lobe level caused by variations in the characteristics of components, without increasing the cost at manufacturing or without causing troubles in the operation.

When a phase amount is set for each of a plurality of antenna elements constituting an array, a phase amount calculated, by adding or subtracting an offset amount to or from a predetermined phase amount is set. Consequently, increase in the side-lobe level of an antenna array caused by the variations in the characteristics of components is reduced electrically, while keeping original components, as they are, without replacing or redesigning them.