A variable power optical system for an endoscope is provided with, in order from an object, a first lens group having a negative power and a second lens group having a positive power and capable of moving along the optical axis. The first lens group includes a negative lens with the concave surface facing an image and a positive lens with the convex surface facing the object in order from the object, and the second lens group includes a cemented lens bonded to a positive lens with the convex surface facing the object. The variable power optical system for an endoscope satisfies the following expressions:0.6 <； fs1 / f1 <； 1.6,1.2 <； ft / fw <； 1.4, and0.5 <； f2 / f1 <； 0.8where f1 [mm] and f2 [mm] represent synthetic focal lengths of the first and second lens groups, respectively； fw [mm] represents a synthetic focal length for the entire system when observing a distant object； ft [mm] represents a synthetic focal length for the entire system when observing an enlarged object； and fs1 represents a focal length of the positive lens closest to the image in the first lens group.
