To avoid the occurrence of a blur in a moving portion while random noise is reduced.

Ultrasonographic image data outputted by each frame from a data processor 13 is inputted to a persistence circuit 14, image data of an input actual frame and output image data of the persistence circuit 14 of the actual frame are inputted to a movement detecting circuit 15 to compare the sizes of both data, it is detected whether or not the absolute value of the difference is larger than a preset value 1, a select circuit 16 is controlled by the output of the movement detecting circuit 15 to select image data inputted to the persistence circuit 14 or image data outputted from the persistence circuit 14, and the selected data is sent to a digital scan converter 17.