An intake system for an internal combustion engine includes plural intake pipes being configured to be connected to cylinders of a main body of the internal combustion engine, respectively, an external gas distribution portion distributing a single type of an external gas to each of the plural intake pipes, a main body of the intake system including the plural intake pipes and the external gas distribution portion, and an external gas introduction passage being integrally formed with the main body of the intake system, the external gas introduction passage being configured to connect the main body of the internal combustion engine to the external gas distribution portion of the main body of the intake system, the external gas introduction passage serving as a single passage being configured to introduce the external gas from the main body of the internal combustion engine to the external gas distribution portion.