PROBLEM TO BE SOLVED: To provide a composition for expansion agent which has a large volume expansion ratio per unit volume and keeps expansion for a long period of time, and to provide an expansion agent using the same.SOLUTION: A composition for expansion agent contains (A) iron powder, (B) metal salt and (C) a powder lubricant, where at least a part of the surface of (A) the iron powder is coated with (B) the metal salt, and a content of (C) the powder lubricant is 0.1 pts.mass or more and 5 pts.mass or less with respect to 100 pts.mass of (A) the iron powder.SELECTED DRAWING: NoneCOPYRIGHT: (C)2018,JPO&INPIT【課題】単位体積当たりの体積膨張率が大きく、かつ膨張が長時間持続する膨張剤用組成物及びそれを用いた膨張剤を提供する。【解決手段】（Ａ）鉄粉と、（Ｂ）金属塩と、（Ｃ）粉末潤滑剤とを含有し、前記（Ａ）鉄粉の表面の少なくとも一部が（Ｂ）金属塩で被覆されており、かつ、前記（Ｃ）粉末潤滑剤の含有量が、前記（Ａ）鉄粉１００質量部に対して０．１質量部以上５質量部以下である、膨張剤用組成物。【選択図】なし
