To understand the effect of quantum stress on energy transfer across scales, we study threedimensional quantum turbulence as described by the Gross-Pitaevskii equation by using the analytical method exploited in the Onsager "ideal turbulence" theory. It is shown that two types of scale-to-scale energy flux exist that contribute to the energy cascade: the energy flux that is the same as in classical turbulence, and that induced by quantum stress. We then propose a definition of the inertial range for quantum turbulence small large , where large is determined through pressure-dilatation and small through quantum-stress-strain. Under assumptions on the regularity of the velocity and density fields, we show that, in the steady state in which the total mean kinetic energy is constant, the classical-type energy flux becomes dominant in i large , while the quantum-type flux becomes dominant in small i, where i is the mean intervortex distance. Correspondingly, the velocity power spectrum exhibits a power-law behavior: