A video signal decoding device comprises a processor, wherein: the processor decodes a sequence parameter set (SPS) raw byte sequence payload (RBSP) syntax included in a bitstream of a video signal, and decodes the bitstream on the basis of the decoding result of the SPS RBSP syntax; the SPS RBSP syntax includes a first syntax element related to the number of one or more sub-pictures configuring one picture, and a second syntax element indicating whether to process a boundary of the one or more sub-pictures as a boundary of the one picture on the basis of the first syntax element; and the second syntax element is parsed only when the number of the one or more sub-pictures is two or more.