An image capturing optical system comprising ten lens elements, the ten lens elements being, in order from an object side to an image side along an optical path, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, a seventh lens element, an eighth lens element, a ninth lens element and a tenth lens element, each of the ten lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side, and a total number of lens elements of the image capturing optical system is ten; wherein the first lens element has positive refractive power, the image-side surface of the second lens element is concave in a paraxial region thereof, the tenth lens element has negative refractive power, and at least one of the object-side surface and the image-side surface of at least one lens element of the image capturing optical system has at least one critical point in an off-axis region thereof; wherein an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the image capturing optical system is ImgH, and the following condition is satisfied: 0.50 < TL / lmgH < 4.0; characterized in that an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element is T45, an axial distance between the fifth lens element and the sixth lens element is T56, a central thickness of the seventh lens element is CT7, an axial distance between the sixth lens element and the seventh lens element is T67, and the following conditions are satisfied: 0 < T12 + T34 + T45 + T56 / T23 < 3.5; and 0.45 < CT7 / T67 < 3.5. wherein the first lens element has positive refractive power, the image-side surface of the second lens element is concave in a paraxial region thereof, the tenth lens element has negative refractive power, and at least one of the object-side surface and the image-side surface of at least one lens element of the image capturing optical system has at least one critical point in an off-axis region thereof; wherein an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the image capturing optical system is ImgH, and the following condition is satisfied: 0.50 < TL / lmgH < 4.0; characterized in that an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element is T45, an axial distance between the fifth lens element and the sixth lens element is T56, a central thickness of the seventh lens element is CT7, an axial distance between the sixth lens element and the seventh lens element is T67, and the following conditions are satisfied: 0 < T12 + T34 + T45 + T56 / T23 < 3.5; and 0.45 < CT7 / T67 < 3.5.