PROBLEM TO BE SOLVED: To provide a light detection unit and a biological information detection device or the like that have high sensitivity and allow size reduction by mounting a light emission part properly on a substrate.SOLUTION: A light detection unit comprises a substrate 160, a light emission part 150 that emits light to an object, and a light receiving part 140 that is attached to the substrate 160 and receives light from the object. The substrate 160 is provided with a hole 169. The light emission part 150 is attached to the hole 169 of the substrate 160.