There is configured a radar or similar device that outputs received data that is currently being received and scan correlated image data in parallel with each other. Scan correlated image data and display image data resulting from received data from a display video memory 13 are input into a transitional data generator 11, and the transitional data generator 11 generates transitional data that represents an intermediate value and gradually changes from the received data into the scan correlated image data, using these signals, and inputs the transitional data into a selector 12. The received data, a FIRST or a LAST signal, and the transitional data are input into the selector 12, and the selector 12 outputs the received data if FIRST=1, and outputs the transitional data if FIRST=0, to the display video memory 13. This image data is fed back to the transitional data generator 11, and therefore it gradually changes from the received data into the scan correlated image data.