To provide a bookmark which surely functions and has a long life and a method for manufacturing it.

In an automatic bookmark with a long life, an amount of bending D of the automatic bookmark and a length L of a dimension of an elastic bending part of 20-70 mm, a height H of 1-5 mm, and a thickness T of 0.2-1.0 mm are provided, and an elastic factor E is selected so that a bending stress σ does not exceed an elastic limit σe×0.95. In addition, a corner is made to be a smooth shape such as round by an injection molding process.