In a beverage dispenser, a beverage material-supplying tube extending from BIB is squeezed by a pump to draw the beverage material from BIB and then to extrude the beverage material to a nozzle. The beverage dispenser has a sensor provided adjacent to the beverage material-supplying tube and a processor into which the output of the sensor is input. The sensor calculates a moving average value using, as a data source, highest signal values among sampled signals obtained by multipoint sampling of analog signals output from the sensor, and, based on the magnitude of a change in the moving average value, a decision is made on whether or not the beverage material has been sold out. By virtue of the above construction, the sold-out of the beverage material in BIB can be accurately detected.