A multi-piece wiring substrate, comprising: a matrix substrate including a first principal face and a second principal face opposite to the first principal face, the matrix substrate being provided with a plurality of wiring substrate regions, the matrix substrate being provided with dividing grooves arranged a long boundaries of the wiring substrate regions in the first principal face and the second principal face, the dividing grooves including first dividing grooves located along respective first sides of the wiring substrate regions in the first principal face, second dividing grooves arranged in the second principal face so as to be opposite to the first dividing grooves, respectively, third dividing grooves located along respective second sides of the wiring substrate regions in the first principal face, and fourth dividing grooves arranged in the second principal face so as to be opposite to the third dividing grooves, respectively, depths of the first dividing grooves and depths of the second dividing grooves being set to be greater than depths of the third dividing grooves and depths of the fourth dividing grooves, first curved parts being provided so that the depths of the third dividing grooves gradually increase as going toward respective corners of the wiring substrate regions, the first curved parts being convexly curved toward the respective corners of the wiring substrate regions, the first curved parts being apart from each other via the third dividing grooves, second curved parts being provided so that the depths of the fourth dividing grooves gradually increase as going toward the respective corners of the wiring substrate regions, the second curved parts being convexly curved toward the respective corners of the wiring substrate regions, the second curved parts being apart from each other via the fourth dividing grooves. a matrix substrate including a first principal face and a second principal face opposite to the first principal face, the matrix substrate being provided with a plurality of wiring substrate regions, the matrix substrate being provided with dividing grooves arranged a long boundaries of the wiring substrate regions in the first principal face and the second principal face, the dividing grooves including first dividing grooves located along respective first sides of the wiring substrate regions in the first principal face, second dividing grooves arranged in the second principal face so as to be opposite to the first dividing grooves, respectively, third dividing grooves located along respective second sides of the wiring substrate regions in the first principal face, and fourth dividing grooves arranged in the second principal face so as to be opposite to the third dividing grooves, respectively, first dividing grooves located along respective first sides of the wiring substrate regions in the first principal face, second dividing grooves arranged in the second principal face so as to be opposite to the first dividing grooves, respectively, third dividing grooves located along respective second sides of the wiring substrate regions in the first principal face, and fourth dividing grooves arranged in the second principal face so as to be opposite to the third dividing grooves, respectively, depths of the first dividing grooves and depths of the second dividing grooves being set to be greater than depths of the third dividing grooves and depths of the fourth dividing grooves, first curved parts being provided so that the depths of the third dividing grooves gradually increase as going toward respective corners of the wiring substrate regions, the first curved parts being convexly curved toward the respective corners of the wiring substrate regions, the first curved parts being apart from each other via the third dividing grooves, second curved parts being provided so that the depths of the fourth dividing grooves gradually increase as going toward the respective corners of the wiring substrate regions, the second curved parts being convexly curved toward the respective corners of the wiring substrate regions, the second curved parts being apart from each other via the fourth dividing grooves.