An air supply device (1) of a stratified scavenging two-cycle engine includes: a mixture passage (40) that penetrates a carburetor (2) and an insulator (3), the mixture passage being provided by a carburetor-side mixture passage (8) and an insulator-side mixture passage (21); a air passage (41) that is provided by a carburetor-side air passage (9) and an insulator-side air passage (22); a throttle valve (13) provided in a single bore (4) of the carburetor (2), the throttle valve(13) being provided by a butterfly valve that rotates in conjunction with a throttle operation; and a flow rate regulator (28) provided inside the air passage (41), the flow-rate regulator (28) bulging inward in the air passage (41). At least a part of a periphery of a valve body (17) of the throttle valve is close to the flow-rate regulator (28) until the valve body (17) is rotated from an initial position corresponding to an idling speed at a predetermined rotation angle.