PURPOSE: To improve performance in the vicinity of a center on a negative as trimming magnification becomes larger and to obtain a picture having excellent image quality from ordinary photographing to trimming photographing.

CONSTITUTION: This photographing optical system is constituted of plural lens groups capable of at least switching a 1st mode (a) in which photographing is executed by setting a 1st image-formation range and a 2nd mode (b) in which photographing is executed by setting a 2nd image-formation range smaller than the 1st image-formation range. In the case of shifting a mode from the 1st mode to the 2nd mode, intervals between plural lens groups are changed and aberration correction is excellently performed with in the 2nd image- formation range.