A radar apparatus where the rate of writing detected image data into an image memory does not decrease, irrespective of an enlarged amount of the detected image data. When an azimuth direction enlargement section of a W data generator receives detected image data of a sweep, it outputs the data to an image memory, and delays the data, depending on a cycle of an azimuth direction shift timing signal. When detected image data of a next sweep is drawn into a pixel adjacent in a sweep moving direction to a pixel into which previous detected image data has been drawn and is located at the same distance in a sweep distance direction, the delayed data is compared with new data, and the greater data is drawn into the new pixel. When the delayed data is greater, this detected image data is enlarged in the azimuth direction.