To prevent an increase in thickness of a bound part of a paper sheet bundle when part of a paper sheet is used to bind the paper sheet bundle.

In a paper sheet processing apparatus, a first hole 5a and a second hole 5b are formed on each of a plurality of paper sheets 5, and engaging pieces 5d are provided on one or more sheets of the paper sheets 5. An engaging part 5f formed of one or two or more stacked engaging pieces 5d of the plurality of stacked paper sheets 5 passes through the second hole 5b after passing through the first hole 5a, to bind the paper sheet bundle 6 formed of the plurality of paper sheets 5. The number of engaging pieces 5d of the engaging part 5f is smaller than that of the paper sheets 5 forming the paper sheet bundle 6.