  We realize the two dimensional anti-de Sitter ($AdS_2$) space as a
Kaluza-Klein reduction of the $AdS_3$ space in the framework of the discrete
light cone quantization (DLCQ). Introducing DLCQ coordinates which interpolate
the original (unboosted) coordinates and the light cone coordinates, we discuss
that $AdS_2/CFT$ correspondence can be deduced from the $AdS_3/CFT$. In
particular, we elaborate on the deformation of WZW model to obtain the boundary
theory for the $AdS_2$ black hole. This enables us to derive the entropy of the
$AdS_2$ black hole from that of the $AdS_3$ black hole.
