  We have measured the thermal conductivity in the $ab$-plane of
La$_{2-x}$Sr$_x$CuO$_4$ ($x =$ 0.10, 0.115, 0.13) in magnetic fields up to 14 T
parallel to the c-axis and also parallel to the $ab$-plane. By the application
of magnetic fields parallel to the c-axis, the thermal conductivity has been
found to be suppressed at low temperatures below the temperature $T_\kappa$
which is located above the superconducting transition temperature and is almost
independent of the magnitude of the magnetic field. The suppression is marked
in $x =$ 0.10 and 0.13, while it is small in $x =$ 0.115. Furthermore, no
suppression is observed in the 1 % Zn-substituted
La$_{2-x}$Sr$_x$Cu$_{0.99}$Zn$_{0.01}$O$_4$ with $x =$ 0.115. Taking into
account the experimental results that the temperature dependence of the
relative reduction of the thermal conductivity is quite similar to the
temperature dependence of the intensity of the incommensurate magnetic Bragg
peak corresponding to the static stripe order and that the Zn substitution
tends to stabilize the static order, it is concluded that the suppression of
the thermal conductivity in magnetic fields is attributed to the development of
the static stripe order. The present results suggest that the field-induced
magnetic order in La$_{2-x}$Sr$_x$CuO$_4$ originates from the pinning of the
dynamical stripes of spins and holes by vortex cores.
