A 2D array transducer 10 is separated into a plurality of sub-arrays. Four representative sub-arrays from SA1 to SA4 are shown in an enlarged manner. In addition, the 2D array transducer (10) is segmented into a plurality of transducer regions. Four regions of (I)-(IV) segmented by dot-and-chain lines represent four transducer regions. For each sub-array, a delay process corresponding to the sub-array is executed based on a delay pattern defining an amount of delay for each of the plurality of transducer elements belonging to the sub-array. In this process, for each transducer region, a common delay pattern is set for the plurality of sub-arrays belonging to the transducer region. For example, because sub-arrays SA1 and SA2 belong to the same transducer region (IV), a common delay pattern is set for the sub-arrays SA1 and SA2.
