A secondary air introduction device configured to introduce air into an exhaust port provided in a cylinder head of an engine by using a negative pressure in the exhaust port, the secondary air introduction device comprising: an air introduction unit having an air introduction passage configured to interconnect an air intake unit for taking therein atmospheric air and the exhaust port; a reed valve provided in the air introduction passage and configured to open and close the air introduction passage in correspondence to a pressure in the exhaust port, the reed valve having a valve body; and a back-flow restriction member (61;71) provided between the reed valve and the exhaust port in the air introduction passage, and comprising a plate part (62;72) having a surface intersecting with an extension direction of the air introduction passage, wherein the plate part (62;72) has an air passing region (63;73) in which the air flowing through the air introduction passage from the air intake unit toward the exhaust port is enabled to pass therethrough, and a back-flow cutoff region (64;74) in which exhaust air, which flows in a direction of directly colliding with at least the valve body of the reed valve, of exhaust air flowing back through the air introduction passage from the exhaust port is cut off, wherein the air passing region (63;73) of the plate part (62;72) is provided with a ventilation structure (66;76) formed by a plurality of aligned holes (65;75), characterized in that the back-flow cutoff region (64;74) of the plate part (62;72) is provided with a ventilation structure (67;77) formed by a plurality of aligned holes (65;75), and the ventilation structure (67;77) provided in the back-flow cutoff region (64;74) has a smaller number of holes (65;75) per a unit area, as compared to the ventilation structure (66;76) provided in the air passing region (63;73). an air introduction unit having an air introduction passage configured to interconnect an air intake unit for taking therein atmospheric air and the exhaust port; a reed valve provided in the air introduction passage and configured to open and close the air introduction passage in correspondence to a pressure in the exhaust port, the reed valve having a valve body; and a back-flow restriction member (61;71) provided between the reed valve and the exhaust port in the air introduction passage, and comprising a plate part (62;72) having a surface intersecting with an extension direction of the air introduction passage, wherein the plate part (62;72) has an air passing region (63;73) in which the air flowing through the air introduction passage from the air intake unit toward the exhaust port is enabled to pass therethrough, and a back-flow cutoff region (64;74) in which exhaust air, which flows in a direction of directly colliding with at least the valve body of the reed valve, of exhaust air flowing back through the air introduction passage from the exhaust port is cut off, wherein the air passing region (63;73) of the plate part (62;72) is provided with a ventilation structure (66;76) formed by a plurality of aligned holes (65;75), characterized in that the back-flow cutoff region (64;74) of the plate part (62;72) is provided with a ventilation structure (67;77) formed by a plurality of aligned holes (65;75), and the ventilation structure (67;77) provided in the back-flow cutoff region (64;74) has a smaller number of holes (65;75) per a unit area, as compared to the ventilation structure (66;76) provided in the air passing region (63;73).