PURPOSE: To provide a rotary valve which increases the cycle efficiency of an engine by reducing a throttle loss to be generated at the time of valve closing and prevents the occurrence of knocking in the case of a gasoline engine and reduces the generation quantity of NOx in the case of a diesel engine.

CONSTITUTION: Guide blades 34a, 34b, 34c, 34d, 34e, 34f for turbulence prevention are provided at the inlet and outlet of a rotary valve 33. The air intake flow passages 33R1, 33R2, 33R3 of the valve body 33-1 of the rotary valve 33 are made up of plural flow passages by using guide blades 33a, 33b. The guide blades for turbulence prevention and the air intake flow passages of the valve body made up of plural flow passages are set so as not to generate contraction flow.