In this paper, we give the definition of pseudo-fiber surface of level n, which is a generalization of pre-fiber surface defined by Kobayashi, and formulate a process for describing unknotting operations for fibered knots with utilizing it. We ask whether the process can always realize the unknotting number of fibered knot (Question 2.1). We generalize Hirasawa’s construction of pre-fiber surface (Proposition 4.1), and Kobayashi’s construction of unknotting number 1 fibered knots (Theorem 5.1). By using these results, we confirm Question 2.1 is positively solved for fibered knots with crossing numbers

fibered knot, unknotting operation, pseudo-fiber surface.