  We discuss a possible interpretation for the pentaquark baryon $\Theta^+$
which has an exotic quantum number of strangeness $S = +1$. The role of the
pion which modifies the structure of single-particle levels of quarks is
examined. When the pion field is sufficiently strong, the ground state of five
quarks for $\Theta^+$ acquires positive parity. If this is the case, an excited
state may appear slightly above the ground state with negative parity.
