A photoelectric conversion element includes in a semiconductor layer a first semiconductor region arranged, a second semiconductor region arranged on a second face side closer than the first semiconductor region and forming a p-n junction with the first semiconductor region to form an avalanche photodiode, a light guide structure including a first portion surrounding a first region and a second portion surrounding a second region inside the first region in a plan view, and an optical structure layer disposed on the second face side. The second portion is disposed over a depth of at least 0.8 μm from the second face, the first and second semiconductor regions are arranged closer to the first face than the second portion, and the second portion overlaps at least a portion of an avalanche multiplication region between the first and second semiconductor region in the plan view.