Treatment agent, flame resistant fiber nonwoven fabric, carbon fiber nonwoven fabric, and methods for producing same

A flame-resistant fiber nonwoven fabric or a carbon fiber nonwoven fabric, comprising a treatment agent for flame-resistant fiber nonwoven fabric production or for carbon fiber nonwoven fabric production adhered thereto, wherein the treatment agent contains a polyether compound in which ethylene oxide and propylene oxide are added to an alcohol, wherein the treatment agent is free of an organic phosphorous compound, the polyether compound has a mass average molecular weight of 8,000 to 40,000, and the alcohol comprises an aliphatic alcohol that is trihydric, wherein the polyether compound is such that when the molar ratio in total of ethylene oxide and propylene oxide added in the molecule is taken as 100% by mol, ethylene oxide is added at a ratio of 25% to 71% by mol to the alcohol and propylene oxide is added at a ratio of 75% to 29% by mol to the alcohol.