To enable a user to create a hardly breakable folding tab at a desired position by using a simple operation.

A hole opening tool for creating a folding tab includes: an insertion port 2 into which a sheet end is inserted; and a punching blade member 21 having a punch blade 22 for opening, in the inserted sheet end, a slit 82 which forms an outer edge of a folding tab 83. Further, both ends 22b of a blade tip 22a of the punch blade have a closed curved shape. Accordingly, a user is enabled to insert a desired sheet end into the insertion port 2 and perform an operation for opening the slit 82 with the punch blade 22, in order to create the hardly breakable folding tab 83 at a desired position by using a simple operation.