I from Belgium too and I'm not 100% sure though, but I think lasers are classified in 4 different classes and not there mW. Belgium is rather severe in these 'gadgets'. I think it's allowed to have class 1 - class 3A lasers, but I'm not sure about 3B - 4.
I suppose Belgium has european legislation without any additional national legislation on this, which would mean you can own a laser of any power output.
Selling anything over 5 mW as a 'laser pointer' is not allowed as they would be hazardous in use.
Legally owning one does not mean you can wave it around though: that could endanger traffic or even be a health hazard for people on the street, and would be an offense it itself.