A weight value used for a beamforming process performed on received signals in an ultrasound imaging apparatus is obtained with a small amount of computations and with a high degree of precision, even when a method of adaptive signal processing is employed.Multiple elements 401 receive ultrasound signals from a test subject, and the similarity operator 404 obtains the similarity between the received signals x(n). By using the similarity C(n) between the received signals obtained by the similarity operator 404, the adaptive weight operator 407 computes the adaptive weight w(n) in association with the similarity. The beamforming operator 408 uses the adaptive weight w(n) and the received signal x(n) to generate a beamforming output. The imaging processor 108 uses the beamforming output to generate image data. By way of example, the similarity operator 404 performs computations of the similarity in the time direction.