Image reading apparatus and control method thereof for determining presence or absence of a document

A control method of an image reading apparatus including a document table on which a document is placed, a pressing plate configured to rotate about a rotation axis between an open position where the document table is uncovered and a closed position where the document table is covered, and a line sensor including an image sensor arranged in a main scanning direction intersecting the rotation axis, and configured to output data by reading the document placed on the document table, the control method comprising:

• calculating threshold data based on first data acquired by the line sensor when the pressing plate is in an intermediate position before reaching the closed position and coefficient data that changes depending on a length from the rotation axis;
• and
• determining presence or absence of the document based on the threshold data and second data acquired by the line sensor when the pressing plate is in the closed position.