PURPOSE: To provide an optical system which executes swing and tilt actions with simple constitution.

CONSTITUTION: This optical system has a first lens system 20 which consists of a thick convex lens 24 as an imaging lens and a planoconcave lens 21 and planoconvex lens 22 provided on the subject 1 side of the front surface thereof and has a prism effect and a second lens system 26 which consists of a planoconcave lens 27 and planoconvex lens 28 provided to face the first lens system 20 and has a prism effect. The thickness at an optical axis O-O changes and the shape just like a prism is obtd. when the planoconcave lens 21 is moved relative to the planoconvex lens 22. The optical axis O-O is thereby curved. The same holds true of the planoconcave lens 27 and the planoconvex lens 28. Consequently, the subject 11 off the optical axis O-O is imaged on an image plane 2. Either one of the first lens system 20 having the prism effect and the planoconvex lens 22 may be provided.