Photographing lens system, image capturing device, and electronic device

A photographing lens system comprising four lens elements, the four lens elements being, in order from an object side to an image side:

• a first lens element with positive refractive power having an object-side surface being convex;
• a second lens element with negative refractive power having an image-side surface being concave;
• a third lens element having an image-side surface being concave, wherein an object-side surface and the image-side surface of the third lens element are both aspheric, and at least one surface of the third lens element has at least one inflection point;
• and
• a fourth lens element with negative refractive power having an object-side surface being concave, wherein the object-side surface and an image-side surface of the fourth lens element are both aspheric;
• wherein the photographing lens system further comprises an aperture stop;
• an absolute value of a curvature radius of an image-side surface of the first lens element is greater than an absolute value of a curvature radius of the object-side surface of the third lens element, there is an air gap between every two of the four lens elements that are adjacent to each other, a curvature radius of the image-side surface of the third lens element is R6, a curvature radius of the object-side surface of the fourth lens element is R7, an axial distance between the aperture stop and the image-side surface of the fourth lens element is SD, an axial distance between the object-side surface of the first lens element and the image-side surface of the fourth lens element is TD, and the following conditions are satisfied:
• −1.0<(R6+R7)/(R6−R7)<1.0;
• and
• 0.75<SD/TD<1.20.