A vacuum belt filter including a belt with a plurality of vacuum boxes, filter means being arranged to the vacuum boxes, drive means for moving the belt, and a suction station for creating an underpressure to the vacuum boxes at the suction station. In order to enable liquid-solid separation at low energy costs and long service interval of the vacuum belt filter, the filter means is in the form of a capillary filter, each vacuum box being provided with such a filter and each vacuum box being provided with an outlet having a check valve enabling a fluid flow from the inside space of the vacuum box to the outside of the vacuum box for creating an underpressure in the vacuum box when the suction station is connected to the vacuum box.