We calculate the energy gap (latent heat) and pressure gap between the hot and cold phases of the SU(3) gauge theory at the first order deconfining phase transition point. We perform simulations around the phase transition point with the lattice size in the temporal direction $N_t=6,$ 8 and 12 and extrapolate the results to the continuum limit. The energy density and pressure are evaluated by the derivative method with nonperturabative anisotropy coefficients. We find that the pressure gap vanishes at all values of $N_t$. The spatial volume dependence in the latent heat is found to be small on large lattices. Performing extrapolation to the continuum limit, we obtain $Delta epsilon/T^4 = 0.75 pm 0.17$ and $Delta (epsilon -3 p)/T^4 = 0.623 pm 0.056.$ We also tested a method using the Yang-Mills gradient flow. The preliminary results are consistent with those by the derivative method within the error.
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