An intake port device comprises an intake port (9) formed by a straight part (13) and a helical part (15), and a valve (17) disposed adjacent to the inlet of the intake port. In order that intake air flow having a large swirl ratio can be supplied to an engine without being encountered with a large resistance even in a light-loaded condition of the engine, the valve (17) is held in its closed position without causing any sharp decrease in the coefficient of intake air flow when closed. In a modification of the intake port device, the valve (17) holds open the lower half of the intake port 9 in its closed position, so that intake air flow having a large swirl ratio can be supplied without being encounted with a large resistance even when the load of the engine is light. In another modification of the intake port device, the free end of the valve (17) is bent and deformed in the downstream direction of intake air so that the flow of intake air may not be encountered with a large resistance.