Ultrasound signal processing device including: transmitter performing transmission events while varying a focal point； receiver generating, for each transmission event, receive signal sequences for transducer elements； delay-and-sum calculator generating, for each transmission event, a sub-frame acoustic line signal including an acoustic line signal for each measurement point located on target lines passing through the focal point and composing a target line group； and synthesizer combining sub-frame acoustic line signals to generate a frame acoustic line signal. The target lines are straight lines, and any measurement point, on any target line, that is spaced away from the focal point by a predetermined distance or more satisfies a condition that distance between the measurement point and a most nearby measurement point on the same target line is smaller than distance between the measurement point and a most nearby one among measurement points on an adjacent target line.
