  The pion exchange between nucleons generates a strong tensor interaction,
which provides a large attractive contribution for the binding energy of
nucleus. This non central tensor interaction is difficult to handle in the
shell model framework, which hinders full understanding of nuclear structure.
We develop the tensor-optimized shell model (TOSM) for the strong tensor
interaction and now we are able to use bare nucleon-nucleon interaction with
the help of the unitary correlation operator method (UCOM) for the short-range
hard core. We adopt the nucleon-nucleon interaction, AV8', and calculate
explicitly the ground state of $^4$He and make a detailed comparison with
rigorous few-body model calculations. We show a large amount of success of the
tensor-optimized shell model with bare nucleon-nucleon interaction for 4He.
