PURPOSE:To evaluate the toughness of a material accurately in a non-destructive manner by using Barkhausen noise (BHN), temper hardness and quenching temperature as parameters and by using a function of the amounts of these parameters. CONSTITUTION:Barkhausen noise (V), hardness (H) and quenching temperature (T) are used as parameters, and the toughness (Ch) of a material is estimated as a function [Ch=f(V, H, T)] of them. The square sum (Vp) of an output voltage of entire BHN generated in a process of magnetization is used as the BHN(V) and the maximum value (Vh) of an instantaneous output voltage of the BHN is used as the BHN (V). As for the material to be applied, SKD5, SKD6, SKD61, SKD62, SKD7, SKD8, etc., are mentioned and the material of which the state of the heat-treated texture has an effect on the BHN is an object. According to this constitution, the toughness can be evaluated in a nondestructive manner.