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). <EOS>