To obtain an imaging system optimum for image pickup devices, especially, for film cameras, video and broadcasting cameras, which reduces blurring of images due to the vibration of a photographing system and has a high focusing speed and a high focusing precision.

The imaging system includes; the photographic system for forming an image of an object; a luminous flux branching means which is placed in an optical path on the image side of a moving lens group for focusing constituting a part of the photographic system and branches a part of a luminous flux passing the moving lens group; a focus detection means which uses the luminous flux branched by the luminous flux branching means to detect an in-focus state of the photographic system; and a control means for controlling drive of the moving lens group. A vibration proof means for suppressing changes of an image position during vibration of the photographic system is disposed on the object side of the luminous flux branching means.