  The standard methods of the magnetic field measurement, based on an analysis
of the relation between the Stokes $V$-parameter and the first derivative of
the total line profile intensity, were modified by applying a linear integral
operator $\hat{L}$ to the both sides of this relation. As the operator
$\hat{L}$, the operator of the wavelet transform with DOG-wavelets is used. The
key advantage of the proposed method is an effective suppression of the noise
contribution to the line profile and the Stokes parameter $V$. The efficiency
of the method has been studied using the model line profiles with various noise
contributions. To test the proposed method, the spectropolarimetric
observations of the A0-type star $\alpha^2\,$ CVn, young O-type star $\theta^1$
Ori C and A0 supergiant HD 92207 were used. The longitudinal magnetic field
strengths for these stars calculated by our method appeared to be in a good
agreement with those determined by other methods.
