To provide an air intake device of an internal combustion engine having a structure capable of discharging blowby oil or fuel coming into an air cleaner case outside of the air cleaner case.

The air intake device 10 of an internal combustion engine 1 injects fuel by an injector 11 while sucking air to feed fuel/air mixture to an air intake port 5 while forming an air circulation channel 31 from a cleaned air chamber 23 of the air cleaner case 20 into the inside of a throttle body 12 having a throttle valve 19 through a funnel 30. A bypass flowing channel 35 other than the air circulation channel 31 is arranged between the cleaned air chamber 23 of the air cleaner case 20 and the throttle body 12 and the bypass flowing channel 35 is constituted such that the flowing channel inlet 35a at the cleaned air chamber 23 side opens to the inner wall face 28a of the air cleaner case 20.