To provide an image input/output system in which an interruption instruction for switching an operation mode to a local mode can be received until a document is placed while an operation in the remote mode is performed by receiving a scan instruction from an external device.

An image input/output device includes: a document detecting section for detecting whether or not a document is placed; an interruption possibility determining section for determining interruption to be impossible when a result of detection indicates the presence of the document in the case where a scanner request is instructed from an input section after the scanner request is received from a host device and for determining interruption to be possible when the result of detection indicates the absence of the document; and a control section for controlling a scanner section to scan the document in the case where interruption is determined to be possible, the detecting section detects the presence of the document, and document reading start is instructed from the input section. If interruption is determined to be impossible, a communication section transmits a notice of reading preparation completion to the host device and when the host device receives the notice, the scanner section scans the document in a driver.