Optical system of real image viewfinder

The object of the present invention is to provide a real image viewfinder optical system with high optical performance and compactness, whose dimension of a whole optical system including an image inverter optical system is small in the thickness direction, and whose dimension to an object side of an eyepiece lens system is small in the thickness direction. A real image viewfinder optical system comprises, in order from an object side, an objective lens system having a positive refractive power as a whole, an eyepiece lens system for observing a real image formed by the objective lens system and having a positive refractive power, and an image inverter optical system for erecting the image to be observed and arranged to an exit pupil side of a lens located to the most object side of the objective lens system and also to the object side of a lens located to the most exit pupil side of the eyepiece lens system. Conditional expressions are satisfied.