The disclosed method of processing a digital broadcast signal comprises generating one RS frame or two RS frames for a data group, forming the data group being divided to 5 data regions, wherein the 5 data regions include a first data region which is located at central of the data group, a second data region which is concentric about the first data region, a third data region which is concentric about the first and second data region, a fourth data region which is concentric about the first, second and third data region and a fifth data region which includes scalable amount of the mobile service data, wherein the fifth data region includes 5 extended data blocks, and wherein data in one of the 5 extended data blocks are merged into the data blocks of the first data region when the one RS frame is generated for the data group.