An ultrasonic signal processing method includes: acquiring pieces of element data output from each element included in an ultrasonic probe including multiple elements configured to transmit an ultrasonic wave to a subject, receive an ultrasonic wave reflected by the subject and output an ultrasonic detection signal; determining element data to be preserved, according to depth information on a reception echo at an acquisition time of the element data, among the pieces of element data of each of the acquired elements; and preserving the element data determined to be preserved.