FIGS. 2A and 2B illustrate that the sheet P is placed on the platen glass 30 such that the crease 70 is perpendicular to the sub-scanning direction DM. The sheet P may only be placed on the platen glass 30 such that the crease 70 intersects the sub-scanning direction DM. A difference between the orientation of the sheet P in the first time and that in the second time does not need to be exactly 180 degrees. That is, the first state may be a state in which the sheet upper side 76 intersecting the crease 70 in the sheet P is directed to the first side Dir1 in the main scanning direction DH, and the second state may be a state in which the sheet upper side 76 is directed to the second side Dir2 in the main scanning direction DH (the opposite side to the first side Dir1).

FIG. 3A is a diagram illustrating (i) first sheet reading (a cross section of the sheet P and the platen glass 30) and (ii) first image information IG1 obtained by reading. FIG. 3B is a diagram illustrating (i) second sheet reading (a cross section of the sheet P and the platen glass 30) and (ii) second image information IG2 obtained by reading. The first image information IG1 and the second image information IG2 illustrated in FIGS. 3A and 3B, and the drawings to be described later are image information of a partial region of the sheet P in the direction along the crease 70, and a magnitude relation of brightness is illustrated in gray scale (it is illustrated that the brightness is higher as it is closer to white).