Provided is a technique capable of simultaneously satisfying two requests of removing a speckle and clarifying a tissue structure. A noise in an ultrasonic image is removed, and a morphology processing is performed on a noise-removed image. The morphology processing includes a first calculation of performing dilation and erosion and a second calculation of performing opening and closing, and determines a value of a structural element used in the second calculation of the morphology by using a result of the first calculation performed on the noise-removed image.