  We propose a simple conformal mechanics model which is classically equivalent
to a charged massive particle propagating near the AdS_2\times S^2 horizon of
an extreme Reissner-Nordstr\"om black hole. The equivalence holds for any
finite value of the black hole mass and with both the radial and angular
degrees of freedom of the particle taken into account. It is ensured by the
existence of a canonical transformation in the Hamiltonian formalism. Using
this transformation, we construct the Hamiltonian of a N=4 superparticle on
AdS_2\times S^2 background.
