The threat was discovered yesterday at lunchtime.
One of the school toilets read: "School shooting on Friday 25 September".
The school reported the incident directly to the police.
Police have been on site and guardians and students have been informed.
- Tomorrow we will have teaching as usual.
But we will have only one entrance and exit where everyone who passes will be inspected.
We will also have guards on site, says principal Patrik Backman.
The text is updated