To provide an inexpensive sheet material positioning device capable of making a positioning position by a first butting member and a third butting member of a sheet material and a positioning position by a second butting member and the third butting member of the sheet material coincide each other, even if there is a bend on an end face of the sheet material.

In an automatic exposure device 10 of a printing plate, a position where the printing plate is butted against a pair of positioning pins 48 and a reference pin 35 when positioning the printing plate in a punch part 16 is made the same as a position where the printing plate is butted against a pair of positioning pins 52 and the reference pin 36 when positioning the printing plate in an exposure part 18. As a result, even if there is the bend on the end face of the printing plate, the positioning position of the printing plate in the punch part 16 and the positioning position of the printing plate in the exposure part 18 can be made to coincide each other, and an exposure position can be made to coincide with a printing position of the printing plate fixed by a punch hole. Further, a cut-out is not required to be punched in the printing plate and a cut-out punching device becomes unnecessary to make the sheet material positioning device inexpensive.