An image reading device reads two types of documents, a first document having a first size and a second document having a second size larger than the first size. A controller of the device causes the first document reader to read the first document and generate image data when the operation unit accepts a command. The first document reader reads a portion of the second document and generates image data on tilt of the second document when the operation unit accepts a command. The document tilt detector detects tilt of the second document based on the image data for detecting tilt of the second document. The document transporter stops transport of the second document when the document tilt detector detects tilt of the second document. The second document reader reads the second document and generates image data when the document tilt detector detects no tilt of the second document.