A reversal of toroidal flow is observed in plasmas where a large positiveelectric field and a sharp electron temperature gradient are sustainedinside the internal transport barrier in a compact helical system.This observation shows that the spontaneous toroidal flow in the directionanti-parallel to the ⟨Er×Bθ⟩ drift becomes large enough to reverse the toroidal flow driven by atangentially injected neutral beam. The difference in the direction and themagnitude of the spontaneous toroidal flow are also discussed.