  A statistically feasible data post-processing method for the conventional
qubit state tomography is studied from an information geometrical point of
view. It is shown that the space $(-1,1)^3$ of the Stokes parameters $(\xi_1,
\xi_2,\xi_3)$ that specify qubit states should be regarded as a Riemannian
manifold endowed with a metric $g_{ij}:=\delta_{ij}/(1-(\xi_i)^2)$, and that
the data processing based on the maximum likelihood method is realized by the
orthogonal projection from the empirical distribution onto the Bloch sphere
with respect to the metric $g_{ij}$. An efficient algorithm for computing the
maximum likelihood estimate is also proposed.
