To obviate a feeling of touching a hard foreign matter in the edge part of a mattress, while maintaining a mattress shape without using a border wire.

Interior trim sheet 2, 3 consisting of urethane foam, felt or the like are superposed on both upper and lower surfaces of a spring unit 1 to be enveloped as a whole by an exterior trim sheet 4. The spring unit 1 has a plurality of pocket coils 10 enveloping coil springs 12 in bag bodies 11 and stood together in large numbers. A band-like cloth sheet is adhered to the upper and lower surfaces of the pocket coils so that the respective pocket coils are connected to each other. The interior trim sheets 2, 3 are adhered unitedly to the upper and lower surfaces of the spring unit 1. The outside pocket coil group 10A of the spring unit 1 compress the pocket coils in the compression direction (vertically) to provide a double decker pocket coil having nearly the same height as the inside pocket coil group 10B so that a spring force larger than the inside pocket coil group 10B is given.