An optical system having a wide angle of view for forming an optical image of a photographic subject on light-receiving surfaces of an imaging element that converts the optical image into an electrical signal comprises a first lens having a negative optical power and a group of lenses each having a positive optical power, which are serially disposed from an object side. The first lens comprises at least one aspherical surface, and has a concave surface centered around an optical axis in vicinity of the optical axis on an image-side surface thereof. Further, an optical entire length T (mm) of the entire system, half angle of view θ, and focal distance ftot (mm) of the entire system satisfy the following conditional expressions. 10 mm