The invention relates to a slimmed-down, small-format, high-zoom-ratio bent type zoom optical system that can be tucked away in a lens mount and an imaging system incorporating the same. The bent type zoom optical system or taking system comprises, in order from its object side, a first lens group G1 of positive refracting power, a second lens group G2 of negative refracting power and a reflecting mirror R located on an image side with respect to the second lens group G2 for bending an optical axis at substantially right angles upon zooming. Between the reflecting mirror R and an imaging plane I there are a plurality of lens groups G2 and G4 interposed. For zooming, while the spacing between the first G1 and the second lens group G2 varies, at least one lens group of the plurality of lens groups G2 and G4 lying on the imaging plane side of the reflecting mirror R moves. The reflecting mirror R remains fixed with respect to the imaging plane I during taking operation, and upon tucked away in a lens amount, the angle of the reflecting mirror R varies such that the normal to the reflecting surface is substantially parallel with the optical axis through the first G1 and the second lens group G2, and the first G1 and the second lens group G2 draw near to the reflecting mirror R with a narrowing spacing between them.