A resolution optimization unit determines an optimal sound velocity corresponding to a tissue component at each position in a scan slice, and calculates a reception delay time or the like for each reception beam from each position in the scan slice. A control processor executes delay addition processing in a scan for acquiring an ultrasonic image actually used for diagnosis by using the reception delay time calculated using an optimal sound velocity. This can correct the difference between the set sound velocity used for the calculation of a reception delay time and the actual in vivo sound velocity and acquire an ultrasonic image with optimized resolution.