To retain thin type and satisfactory image performance despite a high variable power ratio and also to accomplish a wide angle and excellent assemblability.

The real image type variable power observation optical system includes, in order from the object side to the pupil side, an objective optical system S1 having positive refracting power, an inverting optical system S2 composed of a prism P1 for inverting an image formed by the objective optical system S1, and an eye-piece optical system S3 having a positive refracting power. The objective optical system S1 is composed by disposing, in order from the object side to the pupil side, a first group optical system G1 of negative power, a second group optical system G2 of positive power, a third group optical system G3 of negative power and a fourth group optical system G4 of positive power. A variable power operation is carried out by moving at least three of the first group optical system G1 to the fourth group optical system G4 in the direction of an optical axis. The real image type variable power observation optical system satisfies conditional formula: 1.8≤Mf3T/Mf3W≤3, wherein a magnification at the tele-photo end of the third group optical system G3 of the objective optical system S1 is Mf3Tand a magnification at the wide-angle end is Mf3W.

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