An information exchanging method using a two-dimensional code and a two-dimensional code reader. An original sheet is prepared by writing a first two-dimensional code and a second two-dimensional code. The first two-dimensional code is readable by the code reader, whereas the second two-dimensional code is unreadable by the code reader. A monochrome copy sheet is prepared by monochromatically copying the original sheet, so that the monochrome copy sheet includes a third two-dimensional code as a monochrome copy of the first two-dimensional code and a fourth two-dimensional code as a monochrome copy of the second two-dimensional code. Accordingly, the third two-dimensional code is unreadable by the code reader, whereas the fourth two-dimensional code is readable by the code reader. Information exchange is performed by using the original sheet and the monochrome copy sheet.