The percentage of a height of each undulation with respect to a length of the undulation is a unit steepness. A steepness is an average value of unit steepnesses of all undulations in a longitudinal direction at each of different positions in a width direction of a metal sheet. The maximum value of steepnesses in a center section in the width direction is less than or equal to 0.3%. The maximum value of steepnesses in a first edge in the width direction and a maximum value of steepnesses in a second edge section in the width direction are less than or equal to 0.6%. The maximum value of steepnesses in at least one of the first edge section and the second edge section in the width direction is less than the maximum value of steepnesses in the center section in the width direction.