In an intake air rate controlling device including a throttle body, forming an air-intake passage, and a plate-like throttle valve, rotatably supported by the throttle body through a throttle shaft, wherein an intake air rate supplied to an internal combustion engine is controlled by a rotation of the throttle valve, and air-flow controlling means is located on an upper stream side or a lower stream side of the throttle valve for suppressing a variation of a torque, effecting on the throttle valve by a hydrodynamic force generated by an intake air, whereby excellent durability, excellent reliability, and high performances are obtainable.