An ultrasonic diagnostic apparatus uses the pixel value of each of the pixels found in a predetermined range relative to a reference position of image data as input matrix and computes an output value corresponding to the input at its image processing section. Thereafter, the sorting filter of the image processing section sorts the elements of each row of the input matrix on a column by column basis. Then, it extracts a partial matrix having the row including the reference position and surrounding rows from the matrix obtained as a result of the sorting and having a number of rows smaller than number of rows of the input matrix and a number of columns same as the number of columns of the input matrix. Furthermore, it computationally determines the median of the elements of the partial matrix and outputs the median as the output value.