http://answers.unity3d.com/questions/1007886/how-to-set-the-new-unity-ui-rect-transform-anchor.html
なので左上にするなら
public static void SetPivotLeftUp(this RectTransform aRectTransform) { Vector2 vec2 = Vector2.one; vec2.Set(0.0f, 1.0f); aRectTransform.anchorMax = vec2; aRectTransform.anchorMin = vec2; vec2.Set(0.5f, 0.5f); aRectTransform.pivot = vec2; }