Abstract: Method and apparatus for measuring the magnitude of a clamping load applied to a laminated iron core of an electric machine which comprises the steps of introducing a sound wave into a laminated iron core of an electric machine at one end face thereof and immediately generating a first electric signal; producing a second electric signal when the sound wave passes through the core body and reaches the opposite end face thereof; measuring a time interval between the emission of the first electric signal and that of the second electric signal; dividing a distance between both end faces of the laminated iron core by the measured time interval to calculate the velocity of a sound wave vertically propagating through the laminated iron core; and determining the measured magnitude of clamping load applied to said core from the calculated propagating velocity of a sound wave with reference to previously prepared data on a relationship between the magnitude of clamping load applied to the core and the corresponding pro