The Einstein-Hilbert action is rewritten in conformally invariant form by the introduction of a multiplet of scalar fields which is an (N+1)-dimensional representation of anO(1,N) group. A negative-energy difficulty associated with noncompact symmetry of the internal space can be solved by choosing a unit where the gravitational coupling is kept constant. In this unit, the field equations become the same as those of theO(1,N) nonlinear sigma model coupled with gravity.