  We estimate the strength of the induced magnetic field due to the total
induced magnetic moment of the anisotropic ($^3PF^2$) neutron superfluid
interior of neutron stars. The induced magnetic field of the neutron stars is
found as follows. $B^{(in)} = \frac{\eta}{{T_7 - \eta}}B^{(0)}
,\begin{array}{*{20}c}{} & {\eta =} \ \end{array}\frac{{m(^3 P_2
)}}{{0.1m_{Sun}}}R_{NS,6}^{- 3} $ ($T_7$ denotes the interior temperature of
the neutron star in unit of 10$^7$ K). The induced magnetic field will
gradually increase with the temperature of the neutron star decreasing in their
late evolutionary stage. A magnetar may appear in a condition when $T_7 \to
\eta$. The upper limit of the induced magnetic field of $^3P^2$ superfluid is
$3.35 \time 10^{14} \eta$.
