In an ultrasonic examination apparatus (100) of the sector scanning type, a false contour appears in a tomographic image of an object (20) due to a variation of the pixelizing, or digitizing precision over the entire scanning region, especially nearthe central ultrasonic scanning lines. A wobbling processor (64) is provided in an address generator for write operation (6). When the echo signals, orthe image signals obtained by the scanning of the central untrasonic scanning lines are written into pixels of a frame memory, the write-in addresses are processed by the wobbling processor (64) so that the pixelizing precision can be uniformed over the entire scanning region.