A first lens group having positive power and having at least a negative lens having a concave surface facing the image side, a positive lens having a convex surface on the image side thereof, and a cemented lens formed by cementing a negative lens and a positive lens, A third lens group having positive power and having at least a cemented lens formed by cementing a positive lens element, a negative lens element and a positive lens element, from a second lens group having negative power having at least a cemented lens formed by cementing a lens, The variable power optical system for the endoscope is configured to satisfy predetermined conditions.像側に凹面を向けた負レンズ、像側の凸面を向けた正レンズ、負レンズと正レンズとを接合した接合レンズを少なくとも有する正のパワーを持つ第一のレンズ群と、負レンズと正レンズとを接合した接合レンズを少なくとも有する負のパワーを持つ第二のレンズ群と、正レンズ、負レンズと正レンズとを接合した接合レンズを少なくとも有する正のパワーを持つ第三のレンズ群からなる内視鏡用変倍光学系を所定の条件を満たすように構成する。
