There are provided an acoustic wave image generating apparatus for generating a B-mode image having a fixed brightness and a control method thereof. First brightness information (81) indicating the brightness of a first B-mode image in the depth direction of the subject is generated. Positional deviation correction is performed on an acoustic wave echo signal having a positional deviation between the focusing position of acoustic waves and the observation target position, and second brightness information (82) indicating the brightness in the depth direction of the subject is generated from a superposition signal obtained by superimposing an acoustic wave echo signal for which the positional deviation has been corrected and an acoustic wave echo signal without positional deviation. The brightness of the first B-mode image is corrected based on the first brightness information and the second brightness information.