To provide a mixer of air and a fuel of an internal combustion engine in which the length of intake pipes of at least two cylinders can be independently changed.

In the internal combustion engine including at least two throttle bodies having an inlet and an outlet and communicated with the intake pipe with the outlet connected to the cylinder so as to allow the fluid to flow, at least two air chokes which are fitted to the inlet concentrically with the throttle bodies, include a fixed part and a movable part while the movable part is moved concentrically with the fixed part between a position indicating the first height by the air choke and a position indicating the second height higher than the first height by the air choke, and at least two fuel injectors disposed on the air chokes, the mixer for mixing air and the fuel includes at least two individual actuators which are designed to move the movable part between the first and second positions.