PURPOSE: To obtain a tent of arbitrary size, etc., by varying the joining size of a joining part by using a loadable/unloadable button and a slit especially in the adjusting method of sheet size, a sheet, and a button for sheet.

CONSTITUTION: This adjusting method of sheet size, sheet, and button for sheet is constituted in such a way that the joining size of each joining part (36a, 37a) can be varied, and also, the size of the sheet such as the tent, an automotive cover, a table cover, and a sheet for construction, etc., can be varied arbitrarily by forming the slits (38, 39) on at least either the joining parts (36a, 37a) confronting with each other, and mounting the loadable/unloadable button(20) via the slits (38, 39).