In a flame retardant composition containing (poly)phosphoric acid amine salts, the amine excess ratio (mol %) represented by formula (I) is 0.01-10 mol %. In the formula, n represents the number of types of amines in the (poly)phosphoric acid amine salt, and A1-An represent the maximum number of dissociation steps of each amine. Here, the maximum number of dissociation steps is the maximum number of dissociation steps with a base dissociation constant pKb at 25° C. in the 0-13 range. B1-Bn represent the number of mol of the amine when an amine is assumed to be present alone in the (poly)phosphoric acid amine salt.