To provide a stapler which can sew a thin paper bundle through a thicker paper bundle than before with one kind thereof.

A crown part 30a of a staple 30 and a foot part 30b size are formed to an intermediate size in a conventional JIS standard number 10 staple 30' and a JIS standard number 3 staple 10". For instance, the total length L1 of the crown part 30a of the staple 30 is formed longer than 9.48 mm, and shorter than 12.45 mm and further, the total length of a pair of foot parts 30b of the stable 30 is formed to be equal to the total length L1 of the crown part 30a.