  We investigate the role of tensor correlation on the structures of
\nuc{4}{He} and its effect on the doublet splitting in \nuc{5}{He}. We perform
a configuration mixing calculation in the shell model type bases to represent
the tensor correlation for $^4$He. It is found that our model describes the
characteristics of the tensor correlation, which is represented by an admixture
of the $0s_{1/2}$ configuration with a spatially modified $0p_{1/2}$ orbit. For
$^5$He, we solve a coupled OCM equation for an extended $^4$He+$n$ model, while
taking into account the tensor correlation in the $^4$He cluster. It is shown
that the tensor correlation produces the Pauli blocking, in particular, for the
$J^\pi={1/2}^-$ state, and its effect causes about half of the p-wave doublet
splitting in $^5$He. This indicates that the strength of the effective
spin-orbit interaction should be reduced by about half from the conventional
one. We obtain a reliable $^4$He-$n$ interaction, including the tensor
correlation, which further improves the behavior of the $d$- and $f$-wave phase
shifts in the $^4$He+$n$ system.
