A secondary air introduction device is configured to supply air into an exhaust passage of an engine to combust unburned gas contained in exhaust gas. The secondary air introduction device includes: an air introduction passage configured to introduce air into the exhaust passage; and a secondary air valve configured to be attached to an outer surface of a cylinder head of the engine and to control opening and closing of the air introduction passage. The secondary air valve is configured to be attached to an outer lateral surface of the cylinder head on one side in an axial direction of a crankshaft, and the secondary air valve includes an air introduction inlet formed in a position opposite to the outer lateral surface of the cylinder head in the axial direction of the crankshaft.