Provided are an ultrasound image producing method and an ultrasound image diagnostic apparatus that can quickly decide the presence or the absence of influence of refraction, can shorten the time taken for measurement or calculation, can perform measurement or calculation with a small error, and can calculate accurate local sound velocity values. A lattice is set in a region-of-interest, environmental sound velocity values of two or more lattice points located at different positions in a scanning direction of ultrasonic waves are measured as preliminary sound velocity measurement, and main sound velocity measurement that calculates local sound velocity values in lattice points is performed when the difference between a maximum value and a minimum value of the measured environmental sound velocity values is equal to or lower than a predetermined threshold.
