A document reading device comprising: a sheet supply tray on which a document is placed; a reading section (2, 3) that reads the document; a sheet discharge tray that houses the document read by the reading section (2, 3); a U-shaped document conveying path that extends from the sheet supply tray to the sheet discharge tray through the reading section (2, 3) for conveying a document fed from the sheet supply tray and discharging it to the sheet discharge tray; a separation section including a feeding roller that feeds the documents on the sheet supply tray while separating the document one from another and a separation member that is brought into pressure contact with the feeding roller; a document feeding roller pair that is disposed downstream of the separation section; and a reading unit that is disposed inside the U-shaped document conveying path, a regulation wall that is provided downstream of the sheet supply tray and with which a leading edge of the document placed on the sheet supply tray is aligned, a guide member that continues from the regulation wall to form a part of the document conveying path at least between the sheet supply tray and the document feeding roller pair, characterized in that: the regulation wall, the guide member and the separation member are configured as one separation guide unit forming a part of the document conveying path, and the separation guide unit is configured to be detached from and attached to the document conveying path, and the reading unit is configured to be removable from inside the U-shaped document conveying path through an opening of the document conveying path through which the separation guide unit is removed. a sheet supply tray on which a document is placed; a reading section (2, 3) that reads the document; a sheet discharge tray that houses the document read by the reading section (2, 3); a U-shaped document conveying path that extends from the sheet supply tray to the sheet discharge tray through the reading section (2, 3) for conveying a document fed from the sheet supply tray and discharging it to the sheet discharge tray; a separation section including a feeding roller that feeds the documents on the sheet supply tray while separating the document one from another and a separation member that is brought into pressure contact with the feeding roller; a document feeding roller pair that is disposed downstream of the separation section; and a reading unit that is disposed inside the U-shaped document conveying path, a regulation wall that is provided downstream of the sheet supply tray and with which a leading edge of the document placed on the sheet supply tray is aligned, a guide member that continues from the regulation wall to form a part of the document conveying path at least between the sheet supply tray and the document feeding roller pair, characterized in that: the regulation wall, the guide member and the separation member are configured as one separation guide unit forming a part of the document conveying path, and the separation guide unit is configured to be detached from and attached to the document conveying path, and the reading unit is configured to be removable from inside the U-shaped document conveying path through an opening of the document conveying path through which the separation guide unit is removed. the regulation wall, the guide member and the separation member are configured as one separation guide unit forming a part of the document conveying path, and the separation guide unit is configured to be detached from and attached to the document conveying path, and the reading unit is configured to be removable from inside the U-shaped document conveying path through an opening of the document conveying path through which the separation guide unit is removed.