To provide a low price small light weight emission control device for an automobile.

A tip of an exhaust pipe 1 from an engine is branched in a discharge pipe 2 and a delivery pipe 3, and the discharge pipe 2 and the delivery pipe 3 can be alternately switched by valves 4, 5. A hollow body 6 is provided and water is stored in the body 6, a purification body provided with a filtering material 14 or the like on an upper part is arranged horizontally, and a tip of the delivery pipe 3 is opened at a lower position in the body 6. A smoke detector is provided in the exhaust pipe 1 to detect smoke concentration The discharge pipe 2 is opened and the delivery pipe 3 is closed when smoke concentration in exhaust gas is a predetermined value or less, when smoke concentration become above the predetermined value, the valves 4, 5 are switched to close the discharge pipe 2 and open the delivery pipe 3. Since exhaust gas is introduced to the emission control device for purification only when smoke concentration is high, the device can be inexpensive, small and light.