To provide an auxiliary tool for cutting sheet capable of accurately cutting the sheet from a sheet roll with a simple operation.

The auxiliary tool 1 for cutting sheet is provided with a roll support part 14 supporting a sheet roll R having a sheet S to be wound turnably around a horizontal axis center Ra on a main body base 2. A mounting base 9 mounting the sheet S delivered from the sheet roll R is disposed on the main body base 2 at the downstream side of the sheet delivering direction (direction of arrow 24) from the sheet roll R, and a cutter guide groove part 18 which extends to the direction crossing the sheet delivering direction and caved downward is provided on the mounting base 9. The roll support part 14 is turnably pivotally supported on a side frames 3, 3, has parallel axis centers 11a, 11a to each other, and composed of at least two support rollers 11, 11 capable of mounting the sheet roll R.