A composition contains the following components (A), (B), and (C), the component (A) being at least one melamine salt selected from the group consisting of melamine orthophosphate, melamine pyrophosphate, and melamine polyphosphate, the component (B) being at least one piperazine salt selected from the group consisting of piperazine orthophosphate, piperazine pyrophosphate, and piperazine polyphosphate, and the component (C) being a monohydrate of alumina. As disclosed, it is possible to provide a composition that can impart excellent levels of processability/moldability and flame retardancy to a resin by being mixed with the resin.