  It has been recently shown that Nambu-Goto action can be re-expressed in
terms of Cayley's hyperdeterminant with the manifest SL(2,R) X SL(2,R) X
SL(2,R) symmetry. In the present paper, we show that the same feature is shared
by Green-Schwarz sigma-model for N=2 superstring whose target space-time is
D=2+2. When its zweibein field is eliminated from the action, it contains the
Nambu-Goto action which is nothing but the square root of Cayley's
hyperdeterminant of the pull-back in superspace \sqrt{\hyperdet(\Pi_{i
\a\Dot\a})} manifestly invariant under SL(2,R) X SL(2,R) X SL(2,R). The target
space-time D=2+2 can accommodate self-dual supersymmetric Yang-Mills theory.
Our action has also fermionic kappa-symmetry, satisfying the criterion for its
light-cone equivalence to Neveu-Schwarz-Ramond formulation for N=2 superstring.
