Norrköping looked for a while this spring to run home the series but stepped on air during the autumn.
In the last round at home against already sawn off Helsingborg, the team lost 3-4 and only finished in sixth place in a situation when they had a chance to reach a place in Europe.
It has been a turbulent autumn in Norrköping and several leading people have left.
Gustafsson, whose official title is manager, has during the autumn referred to the fact that he had one year left on the contract.
- In this way, I want to thank everyone who made these five years in IFK Norrköping into unforgettable years. Thanks to all the players and leaders who worked tirelessly to develop both the team and the organization. I would like to extend a special thank you to all our supporters who have strongly contributed to my best memories of the club, says Gustafsson to Norrköping's website.