  We study the Kaluza-Klein spectrum of D=5 simple supergravity on $S^2$ with
special interest in the relation to a two-dimensional N=4 superconformal field
theory. The spectrum is obtained around the maximally supersymmetric
Freund-Rubin-like background $AdS_3\times S^2$ by closely following the
well-known techniques developed in D=11 supergravity. All the vector
excitations turn out to be ``(anti-)self-dual'', having only one dynamical
degree of freedom. The representation theory for the Lie superalgebra
$SU(1,1|2)$ is developed by means of the oscillator method. We calculate the
conformal weight of the boundary operator by estimating the asymptotic behavior
of the wave function for each Kaluza-Klein mode. All the towers of particles
are shown to fall into four infinite series of chiral primary representations
of $SU(1,1|2)\times SL(2,{\bf R})$ (direct product), or $OSp(2,2|2;-1)\cong
SU(1,1|2)\times SL(2,{\bf R})$ (semi-direct product).
