To predict the iron loss of a non-oriented electrical steel sheet after shearing, a non-oriented electrical steel sheet is sheared to a certain width, and iron loss Wt(B0) of the non-oriented electrical steel sheet after shearing is estimated according to a predetermined relational expression based on iron loss Wn(B1) in a non-machining-affected zone in which no machining strain is introduced by the shearing and iron loss Wi(B2) in a machining affected zone in which machining strain is introduced.