To provide an image pickup optical system, capable of making a finder optical system small in size, consequently, making a camera into a small size.

For this image pickup optical system, a primary image formed by an objective lens 1 is reduced and re-formed on an imaging device 4 by reflection mirrors 5, 6 and 7 and a secondary image forming lens 3, and then the image is picked up. The finder optical system provided with a reticle 9 and an eyepiece 10 is arranged behind the secondary image forming lens 3, and a movable mirror 8 for selectively distributing the light from the secondary image forming lens 3 to the imaging device 4, and the finder optical system is arranged.