A sheet transport device including: a transport path in which a sheet (P) passes; a transport guide member constituting the transport path so as to guide the sheet (P); and a detection mechanism disposed in the transport path so as to detect presence or absence of the sheet (P), the detection mechanism including an actuator portion configured to swing when abutting the sheet (P), and a sensor portion configured to detect swinging of the actuator portion , the actuator portion including a shaft portion extending in a width direction of the sheet (P), which is orthogonal to a transport direction of the sheet (P), and a detection portion disposed to protrude outward in the radial direction from the shaft portion so as to swing about the shaft portion in a transport direction when abutting the sheet (P), wherein the transport guide member includes a base portion , and a plurality of first guide ribs standing on the base portion at a predetermined interval in the width direction of the sheet (P) so as to guide the sheet (P), the first guide ribs are provided with a notch portion through which the shaft portion of the actuator portion penetrates, characterized in that the shaft portion is provided with a plurality of second guide ribs protruding outward in the radial direction from the shaft portion , the second guide ribs are disposed so as to overlap an opening of the notch portion viewed from an axis direction of the shaft portion , thereby to prevent the sheet (P) from entering the notch portion , and one of the first guide ribs is disposed between two adjacent ones of the plurality of second guide ribs . a transport path in which a sheet (P) passes; a transport guide member constituting the transport path so as to guide the sheet (P); and a detection mechanism disposed in the transport path so as to detect presence or absence of the sheet (P), the detection mechanism including an actuator portion configured to swing when abutting the sheet (P), and a sensor portion configured to detect swinging of the actuator portion , the actuator portion including a shaft portion extending in a width direction of the sheet (P), which is orthogonal to a transport direction of the sheet (P), and a detection portion disposed to protrude outward in the radial direction from the shaft portion so as to swing about the shaft portion in a transport direction when abutting the sheet (P), wherein the transport guide member includes a base portion , and a plurality of first guide ribs standing on the base portion at a predetermined interval in the width direction of the sheet (P) so as to guide the sheet (P), the first guide ribs are provided with a notch portion through which the shaft portion of the actuator portion penetrates, characterized in that the shaft portion is provided with a plurality of second guide ribs protruding outward in the radial direction from the shaft portion , the second guide ribs are disposed so as to overlap an opening of the notch portion viewed from an axis direction of the shaft portion , thereby to prevent the sheet (P) from entering the notch portion , and one of the first guide ribs is disposed between two adjacent ones of the plurality of second guide ribs . <EOS>