  The superconducting gap structure of LaFePO ($T_c=7.4 $K) is studied by
thermal conductivity ($\kappa$) at low temperatures in fields $H$ parallel and
perpendicular to the c axis. A clear two-step field dependence of $\kappa(H)$
with a characteristic field $H_s(\sim 350$ Oe) much lower than the upper
critical field $H_{c2}$ is observed. In spite of large anisotropy of $H_{c2}$,
$\kappa(H)$ in both $H$-directions is nearly identical below $H_s$. Above
$H_s$, $\kappa(H)$ grows gradually with $H$ with a convex curvature, followed
by a steep increase with strong upward curvature near $H_{c2}$. These results
indicate the multigap superconductivity with active two-dimensional (2D) and
passive 3D bands having contrasting gap values. Together with the recent
penetration depth results, we suggest that the 2D bands consist of nodal and
nodeless ones, consistent with the extended s-wave symmetry.
