a rocker arm includes : a body that is made of sheet metal and includes a pair of side walls ; and a pair of axial holes that are respectively formed through the pair of side walls and have a first diameter and through which an axis is inserted . the pair of axial holes include thickened portions formed partially or overall of circumference of the pair of axial holes , and the thickened portion is formed by expanding a hole that has a second diameter smaller than the first diameter and is formed in a pre - arranged range for forming the axial hole in a blank material so as to causing plastic flow in a metallic material of the circumference of the hole