PURPOSE: To improve the picture quality of successive scanning output signals by executing successive scanning conversion in a band to which a compensation signal is not transmitted by means of a letter box type decoder based upon signals corresponding to respective frames as units and executing successive scanning conversion by using twice the information quantity of a signal obtained by intra-field interpolation.

CONSTITUTION: A main screen part signal in a signal arriving by a letter box system and jump scanning is synthesized with a frame by a frame synthesizing circuit 302 and separated into a high band component and a low band component by a V-HPF 303 and a subtractor 304. In the case of a still image, a switch 306 is turned on, the high band component is added by an adder 305 and conversion into successive scanning is executed by a double speed conversion and a selector, and in the case of a dynamic image, a vertical high band component is shifted to a low band by a V shifting circuit 307 and conversion processing into successive scanning is executed by the shifted component and the low band component from an adder 304.