1. A picture processing device for performing a process of superposing a sub picture image on a moving picture image which forms a base, comprising: a detection unit configured to detect, based on the sub picture image, a region of the moving picture image in which a movement amount is small, out of a plurality of regions in which the sub picture image may be superposed on the moving picture image; a picture image superposing unit configured to superpose, via a processor, the sub picture image on the region in which the movement amount is small; a main processor configured to process the moving picture image; and a sub processor configured to process the sub picture image wherein in the moving picture image, a plurality of picture images are divided into a plurality of blocks such that each picture image includes a predetermined number of pixels, and subjected to a predetermined compression process, the detection unit obtains motion vector information from a block of each picture image included in the moving picture image and calculates a region in which a variation of the movement amount between picture images in the moving picture image is small, the detection unit calculates a total sum of movement amounts per predetermined number of block units and successively compares the total sum between the adjacent blocks while sequentially scanning the blocks in a predetermined direction to calculate a region in which the total sum becomes small, and the image superposing unit superposes the sub picture image obtained from the sub processor on the region of the moving picture image obtained from the main processor.