A flame retardant composition comprising 1-99 weight parts of a salt of piperazine and an inorganic compound selected from among piperazine phosphate, piperazine pyrophosphate and piperazine polyphosphate, or a mixture of two or more of these piperazine salts (ingredient (A)), 99-1 weight parts of a salt of melamine and an inorganic compound selected from among melamine phosphate, melamine pyrophosphate and melamine polyphosphate, or a mixture of two or more of these melamine salts (ingredient (B)) (wherein, the sum of ingredient (A) and ingredient (B) is 100 weight parts), 0-50 weight parts of an arbitrary ingredient (ingredient (C)), and 0.01-20 weight parts of a silicone oil having a viscosity at 25° C. of 5000 mm2/s or less(ingredient (D)) which is added to the composition comprising the aforementioned ingredients (A)-(C) and treats them.