To provide polyphosphate salt of a 1, 3, 5-triazine compound, which is suitable when used as a flame retardant in a polymer and exerts no bad influence on the mechanical strength of the polymer.

The polyphosphate salt of the 1, 3, 5-triazine compound is characterized in that the number-average degree n of condensation is larger than 20 and the melamine content is higher than 1.1 mole per one mole of phosphorus atom.