According to one embodiment, an edge-smoothing apparatus has a synthesizing unit that generates a main synthesized video signal representing different images, a flag-inserting unit that inserts ID flags into the video data items, respectively, an image-edge processing unit that outputs a reference synthesized video signal from the main synthesized video signal, and selects and outputs a plurality of edge-smoothing synthesized video signals in accordance with a selection signal. A flag decoder discriminates the ID flags and generates the selection signal to prevent the edge-smoothing synthesized video signals for the different images, from being processed together, and generates an edge-smoothing-parameter selecting signal in accordance with the ID flags. Edge-smoothing components are generated by using the reference synthesized video signal from the image-edge processing unit and the edge-smoothing synthesized video signals. The edge-smoothing components, thus generated, are adjusted with a parameter selected.