A method is offered which is capable of quantifying all the peaks of a magnetic resonance spectrum based on a theoretical relationship between the real and imaginary parts of the spectrum without phase correcting the peaks. First, the spectra of the real and imaginary parts are found by quadrature detection. Then, integrated values a and b over given regions of the obtained spectra of the real and imaginary parts, respectively, are found. An integral intensity of a spectral peak in the spectrum is calculated to be .+-.{square root}{square root over ((a.sup.2+b.sup.2))}.