An intake system for an engine includes a duct defining an intake passage therein, and a cantilevered valve including a valve main body opening/closing the intake passage, a shaft supporting the body, and a valve extension portion. The duct includes a reduced passage portion between the duct and the body when the body is in a fully closed position, a recess accommodating the body and the extension portion when the body is fully opened, and a pressure introduction passage formed between the duct and the body when the body is fully closed, and communicating with a space between the body and the extension portion when the body is fully closed. The extension portion includes a sealing part. The duct and the sealing part define a clearance therebetween when the body is fully closed. The clearance has a smaller sectional area than the reduced passage portion.