a document conveyor that conveys a document including at least one page;

an image reader that reads an image of the conveyed document;

at least one main memory that each includes an image memory that stores image data of each read page and a system memory that stores a processing program;

a data transfer circuit that performs image data transfer from the image reader to the image memory; and

one or more controllers that each control reading of the image in accordance with the processing program and establish a setting of the data transfer circuit related to the image data transfer, whereas

the controllers determine whether to read an image of each page in a first reading mode or a second reading mode before start of conveyance of a next document, the first reading mode being a mode in which conveyance of the next document is started before reading of an image of a previous page is completed while an image of a document including a plurality of pages is read page by page, the second reading mode being a mode in which conveyance of the next document starts after reading of the document of a previous page is completed while the image of the document including the plurality of pages is read page by page, and

when there is a possibility that preparation regarding image data transfer of the next page is not completed during reading in the first reading mode, the first reading mode is switched to the second reading mode to read an image of the next page.