Provided are a wiring substrate; a multi-piece wiring substrate array; and a method for reliably producing the multi-piece wiring substrate array. The wiring substrate includes a substrate main body, which has first and second main surfaces, side surfaces, a groove surface, and a fracture surface; and a notch which has a concave shape in plan view, and which is provided on a side surface on a side toward the first main surface, wherein, in the side surface having the notch, the boundary between the groove surface and the fracture surface has first curved portions on opposite sides of the notch, the first curved portions being convex toward the first main surface in side view; and also has a second curved portion on a second-main-surface side of the notch, the second curved portion being convex toward the second main surface of the substrate main body in side view.