A sample tube is washed by inserting a suction tube from an open end of the sample tube having a closed end, and circulating washing liquid supplied from an upper side of the closed end of the sample tube over an exterior and in an interior of the sample tube to suck and discharge the liquid through the suction tube. The sample tube is washed by providing a holder for holding the sample tube in a manner that the open end of the sample tube having a closed end, the suction tube of which upper end side is inserted to the sample tube and of which lower end side is supported by the holder, and a washing liquid receiving tube arranged around the sample tube, and by circulating the washing liquid supplied from the upper side of the closed portion of the sample tube over the exterior and in the interior of the sample tube to suck and discharge the liquid through the suction tube. On the other hand, the sample tube is dried by circulating air over the exterior and in the interior of the sample tube after the washing.
