We prove, for any $β>0$, a central limit theorem for the fluctuations of linear statistics in the Sine-$β$ process, which is the infinite volume limit of the random microscopic behavior in the bulk of one-dimensional log-gases at inverse temperature $β$. If $φ$ is a compactly supported test function of class $C^4$, and $\mathcal{C}$ is a random point configuration distributed according to Sine-$β$, the integral of $φ(\cdot / \ell)$ against the random fluctuation $d\mathcal{C} - dx$, converges in law, as $\ell$ goes to infinity, to a centered normal random variable whose standard deviation is proportional to the Sobolev $H^{1/2}$ norm of $φ$ on the real line. The proof relies on the DLR equations for Sine-$β$ established by Dereudre-Hardy-Maïda and the author, the Laplace transform trick introduced by Johansson, and a transportation method previously used for $β$-ensembles at macroscopic scale.