  Using a modification of the Shapiro scaling approach, we derive the
distribution of conductance in the magnetic field applicable in the vicinity of
the Anderson transition. This distribution is described by the same equations
as in the absence of a field. Variation of the magnetic field does not lead to
any qualitative effects in the conductance distribution and only changes its
quantitative characteristics, moving a position of the system in the
three-parameter space. In contrast to the original Shapiro approach, the
evolution equation for quasi-1D systems is established from the generalized
DMPK equation, and not by a simple analogy with one-dimensional systems; as a
result, the whole approach became more rigorous and accurate.
