Packed-bed reactors filled with ion-exchange resin catalysts are very effective for the continuous production of various chemicals. However, the resin tends to swell or shrink depending on the composition of the surrounding solution, and this can greatly alter the resin bed height and the volume of the liquid phase above the resin in a fixed-volume reactor. Because this liquid phase does not contribute to the production of chemicals in the reaction, it is important to minimize the liquid-phase volume to increase the productivity. In the present study, an adjustable-volume packed-bed reactor system was developed, and its effectiveness for the continuous production of fatty acid esters and regeneration of the resin were evaluated. The column height was adjusted by controlling the position of a movable plunger to minimize the liquid-phase volume in the upper part of the column. In fatty acid ester production using the adjustable-volume reactor, the residence time of the reactants in the liquid phase was shorter than that in a fixed-volume reactor, and the solution was rapidly eluted from the column, which improved productivity. For resin regeneration, minimization of the liquid-phase volume in the adjustable-volume reactor reduced the effect of dilution on the performance of the regeneration solutions compared to that in the fixed-volume reactor, and less regeneration solution was required. The adjustable-volume reactor could allow for more efficient and environment-friendly production of chemicals than a fixed-volume reactor.