An internal combustion engine wherein when an aqueous urea solution should be fed from an aqueous urea solution feed valve (8), a feed pump (9) is operated forward and aqueous urea solution in an aqueous urea solution tank (4) is fed through an aqueous urea solution feed passage (10) into the aqueous urea solution feed valve (8). When ceasing the feed of aqueous urea solution from the aqueous urea solution feed valve (8), the feed pump (9) is operated in reverse whereby the ammonia gas generated in the aqueous urea solution tank (4) is drawn through a ammonia gas feed pipe (11) into the aqueous urea solution feed passage (10). Next, when the feed pump (9) is operated forward, the ammonia gas drawn into the aqueous urea solution feed path (10) is ejected from the aqueous urea solution feed valve (8).