PURPOSE: To make it difficult to confirm a boundary of a block on a screen, to contain the processing in the block, and to realize a high degree of secrecy against illegal decoding by determining successively the number of lines of the block of a scanning line transfer and the processing contents in each block.

CONSTITUTION: A random number generating circuit 5 which is shifted successively by an input of a control information input terminal 4 to which control information for giving the processing contents of a video signal is inputted and generates a random number, a block latch pulse generating circuit 6, a latch 7, an in-block address generating circuit 8, etc., are provided. In this state, in accordance with the number of lines of a block of a scanning line transfer determined successively by the random number generating means 5 and data for designating the processing contents in the block, the scanning line transfer is executed in each block. In such a way, by determining successively the number of lines of the block by the random number, the blocks consisting of a different number of lines are mixed. Accordingly, in the case a processed video signal is displayed on a monitor, it becomes impossible to easily confirm a boundary of the blocks on the screen, and the degree of secrecy against illegal decoding can be secured.