To add flame retardancy to a plastic without combining halogen elements and without using compounds of antimony and phosphorus in addition to the plastic.

The use of a polymer containing at least 1 wt.% of nitrogen with ≥0.1 wt.% to ≤10 wt.% of bismuth oxide prevents flame growth considerably and even if the composition catches flame, flame can be put off easily and burning is immediately extinguished. The composition does not damage the properties of the plastic. This composition has flame retardancy without including other conventional flame retarding materials containing halogen elements and phosphorus.