Disclosed is a polyolefin-based resin composition having excellent heat resistance and excellent flame retardancy. Specifically, provided is a flame-retardant polyolefin-based resin composition which includes a polyolefin resin and, incorporated thereinto, component (A), which is one or more melamine salts selected from the group consisting of melamine orthophosphate, melamine pyrophosphate, and melamine polyphosphate, component (B), which is one or more piperazine salts selected from the group consisting of piperazine orthophosphate, piperazine pyrophosphate, and piperazine polyphosphate, and component (C), which is a compound represented by general formula [1] and/or a compound represented by general formula [2]. Details of the general formulae [1] and [2] are as described in the description.