In an intake system for an engine that includes plural throttle bodies 2 to 4 having throttle valves for changing an intake passage area, the plural throttle bodies 2 to 4 include manually driven side throttle bodies 2 to 4, which have manually driven side throttle valves 2b to 4b that are opened and closed by a throttle operation of a rider, and an electrically driven side throttle body 5, which has an electrically driven side throttle valve 5b that is opened and closed by an electric motor 11, and the intake system includes a valve opening control means 15 that controls an opening of the electrically driven side throttle valve 5b such that a specific output characteristic corresponding to an operating state of an engine is obtained.