It is suggested that energetic particles populating the Jovian outer magnetosphere and neighboring interplanetary space are flowing out from the Jovian radiation belt by the outward diffusion process that violates both second and third adiabatic invariants. This cross-field diffusion process operates preferentially at low altitudes, and it does no cause serious degradation of particle energy. A model is constructed which combines this process with ordinary inward diffusion and pitch angle scattering, and it is found to compare favorably with Pioneer 10 observations in the Jovian magnetosphere.