PURPOSE: To measure the concentration of paste liquid, which is attached to warp, accurately.

CONSTITUTION: A paste-liquid picking device 13 picks up the sample of paste liquid (s) from a sizing device into a container 24. A drying device 25 heats the paste liquid sample in the container 24 in order to obtain only the solid state paste in the absolute dry state. A weighing device 20 measures the weight of the paste liquid sample in the container or the weight of the solid state paste in the absolute dry state. The paste liquid sample is picked up with the paste-liquid picking device 13. The weight of the paste liquid sample is measured with the weighing device 20, and the measured value is stored. Then, only the solid state paste in the absolute dry state is obtained from the paste liquid sample with the drying device 25. The weight of the solid-state paste in the absolute dry state is measured with the weighing device 20, and the measured value is stored. The concentration of the paste liquid is computed based on both stored measured values with a control device 30, and the result is outputted.