Light-reflective concave portions are disposed on the surface of a substrate. The concave portions have a first and second vertical section perpendicular to each other. The first vertical section has an internal shape defined by a first curve and a second curve, the first curve extending from one point on the peripheral edge of the concave portion to the deepest point of the concave portion, and the second curve extending continuously from the first curve and from the deepest point of the concave portion to another point on the peripheral edge of the concave portion. The average of the absolute value of an inclination angle of the first curve is larger than that of the second curve relative to the substrate surface. The second vertical section has an internal shape defined by a shallow curve and deep curves formed at both sides of the shallow curve.