An ultrasound signal processor that selectively drives a plurality of transducer elements arrayed in an ultrasound probe and executes ultrasound transmission and reception to a subject to perform velocity analysis by a color flow mapping method includes: a transmitter configured to select a transmission transducer element array from the plurality of transducer elements and perform transmission from the transmission transducer element array； a receiver configured to generate a received signal sequence for a transducer element of a reception transducer element array； a phasing adder configured to generate an acoustic line signal； and a velocity calculator configured to generate a complex acoustic line signal and calculate an average velocity, wherein the phasing adder performs delay processing for changing a method for calculating a transmission time in which the ultrasound transmitted reaches each of the observation points in at least one of the main target area and the sub-target area.
