A combustible gas enrichment system includes an adsorption unit charged therein with an adsorbent for selectively adsorbing a combustible gas, a source gas feeding means capable of feeding source gas containing the combustible gas into the adsorption unit from the outside, a suctioning means capable of suctioning the gas from the inside of the adsorption unit and a controlling means for executing an adsorption process for feeding the source gas into the adsorption unit for adsorption of the combustible gas to the adsorbent and a desorption process for desorbing the combustible gas from the adsorbent under the suction force of the suctioning means after the adsorption process and taking the desorbed combustible gas to the outside. The controlling means operates the suctioning means such that the suction force of the suctioning means when no desorption process is effected is smaller than the suction force when the desorption process is effected.