An ultrasound diagnostic device includes: an ultrasound probe which transmits ultrasound toward a tested subject by a plurality of transducers and obtains a received signal； a beam forming section for adding the received signal for each of the transducers with matching a phase of the received signal； an image processing section which generates an image data； a coherent factor calculation section which calculates a coherent factor which represents a ratio of a coherent sum to an incoherent sum； a coherent factor correction section which corrects the coherent factor so as not to be smaller than a predetermined value； and a signal correction section which correct the received signal after having been subject to the adding, by multiplying the received signal after having been subject to the adding by the coherent factor corrected by the coherent factor correction section as a coefficient.
