  We study the characteristics of the tensor correlation in $^4$He using a
shell model type method. We treat the tensor force explicitly by performing a
configuration-mixing calculation in the $2p2h$ basis and include
single-particle states up to intermediately high angular momenta. We adopt the
Gaussian expansion method for the quantitative description of the spatial
shrinkage of the single-particle states to optimize the tensor correlation. We
are able to describe the full strength of the tensor correlation for $^4$He in
the shell model type method by realizing convergence. We call this model the
tensor-optimized shell model. It is found that in $^4$He, three specific $2p2h$
configurations are strongly coupled with the $(0s)^4$ configuration due to the
characteristic features of the tensor operator.
