  We introduce the infinite-dimensional Lie superalgebra ${\mathcal A}$ and
construct a family of mappings from certain category of ${\mathcal A}$-modules
to the category of A_1^(1)-modules of critical level. Using this approach, we
prove the irreducibility of a family of A_1^(1)-modules at the critical level.
  As a consequence, we present a new proof of irreducibility of certain
Wakimoto modules. We also give a natural realizations of irreducible quotients
of relaxed Verma modules and calculate characters of these representations.
