An image capturing optical system includes seven lens elements, the seven lens elements being, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element. An image-side surface of the fifth lens element is convex in a paraxial region thereof. An image-side surface of the sixth lens element is concave in a paraxial region thereof. The seventh lens element has negative refractive power.