Patented is a sheet member, comprising  a first sheet; a second sheet; and at least one elastic member having a shape selected from a thread shape, a net shape, a strip shape, and a sheet shape, arranged between the first sheet and the second sheet;  wherein the first sheet comprises:
a plurality of high-density regions; and a plurality of low-density regions, wherein the high-density regions alternate with the low-density regions in a predetermined direction.

The elastic member is arranged in the predetermined direction in which the plurality of high-density regions alternate with the plurality of low-density regions and the elastic member in an expanded state is attached to at least a part of each of the plurality of high-density regions, and the following equation is satisfied:
(A+C)/X≧A