Scan device capable of detecting an open/close state of a cover

A scan device includes a body, a scanning module disposed in the body, a cover pivotably connected to the body, an optical sensor and a power supply controller. The body has a scan platen, on which a document may be placed. The optical sensor for receiving ambient light and correspondingly outputting an open-state signal is disposed on the cover or body. The power supply controller electrically connected to the optical sensor controls power supplied to the scanning module according to the open-state signal.