To use a replaceable sheet itself as a mark without separately preparing a bookmarker or the like by filing a sheet in a vertically or laterally movable state.

The replaceable sheet comprises a plurality of locking pawl inserting holes 12 opened along a vertical direction at a left side edge part 10a of a replaceable form 10. Locking pawls of a system notebook are respectively inserted into the holes 12. The each hole 12 is formed in a gourd-like state by continuously providing a circular first locking pawl hole 12A formed at an upper side to a circular second locking pawl hole 12B formed at a lower side. And, locally contracted part 12C is formed between the hoes 12A and 12B.