Image reading device, storage medium, and image forming system

An image reading device comprising:

• a reading conveyor;
• a reading scanner configured to read an image of a sheet conveyed by the reading conveyor during conveyance;
• and
• a hardware processor,
• wherein,
• the hardware processor performs control such that, from an adjustment chart in which one mark or a plurality of marks are formed, the one mark having a plurality of oblique sides whose widths change in a main scanning direction or a sub-scanning direction and which are symmetrically shaped with respect to a center line in the main scanning direction and the plurality of marks include the oblique side, the one mark or the plurality of marks are read at two or more locations in a reading line that is one or more pixels in the sub-scanning direction and that includes pixels corresponding to a width of the adjustment chart in the main scanning direction at intervals in the sub-scanning direction,
• the hardware processor calculates an inclination in the main scanning direction from a difference in a mark width in one read line that has been read, and
• the hardware processor calculates the inclination in the sub-scanning direction from the difference in a position or a width of the mark in the two reading lines which are read with the interval in the sub-scanning direction.