A light-emitting-element mount substrate formed by relatively simple manufacturing steps, having a good heat release property, and having a high mechanical strength; and an LED device including the light-emitting-element mount substrate are provided. A substrate body of a light-emitting-element mount substrate is made of a low-resistance semiconductor (e.g., n-type silicon) substrate, and is divided into a first and second individual substrate bodies by an insulating layer. A first front-surface mounting electrode and a first external-connection electrode are formed on respective first and second major surfaces (e.g., front and back surfaces) of the first individual substrate body. A second front-surface mounting electrode and a second external-connection electrode are formed respective first and second major surfaces (e.g., front and back surfaces) of the second individual substrate body. The insulating layer has a shape different from a straight-line shape in plan view.