In this paper, we study the irreducible highest weight module
L(Λ
0) of affine Lie algebra
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. Since the three-dimensional simple algebra sl
2 is regarded as a Lie subalgebra of
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,
L(Λ
0) naturally becomes a sl
2-module. We present the irreducible decomposition of
L(Λ
0) as a sl
2-module.