A flame retardant composition containing a piperazine phosphate, a melamine phosphate, and an oil having a siloxane bond and a specific gravity of 0.930 to less than 0.970 at 25° C. The oil is present in an amount of 0.01 to 5 parts by mass per 100 parts by mass of the sum of the piperazine phosphate and the melamine phosphate. The flame retardant composition preferably further contains 0.01 to 5 parts by mass, per 100 parts by mass of the sum of the piperazine phosphate and the melamine phosphate, of a methylhydrogen silicone oil having hydrogen as part of the side chains of polysiloxane and a specific gravity of 0.970 to less than 1.01 at 25° C.