A tissue treating apparatus, which supplies different kinds and different concentrations of liquid chemicals to and discharges the same, in a predetermined order, the order being ethanol, xylene and then paraffin, from a processing chamber containing a tissue specimen so as to perform a tissue specimen infiltration treatment, comprising: the processing chamber for containing the tissue specimen; a plurality of liquid-chemical reservoirs (14, 16, 18) being connected to the processing chamber by liquid-chemical pipes, the liquid-chemical reservoirs (14, 16, 18) storing the liquid chemicals to be used for infiltration-treating the tissue specimen contained in the processing chamber, the liquid chemicals being ethanol, xylene and paraffin, each at different concentrations; characterized in that the apparatus includes a first cleaning liquid reservoir being connected to the processing chamber by a first cleaning liquid pipe, the first cleaning liquid reservoir storing ethanol which cannot be used for the infiltration treatment of the tissue specimen as an ethanol cleaning liquid; a second cleaning liquid reservoir being connected to the processing chamber by a second cleaning liquid pipe, the second cleaning liquid reservoir storing xylene which cannot be used for the infiltration treatment of the tissue specimen as a xylene cleaning liquid; a supply/discharge port for supplying liquid chemical to and discharging the same from the processing chamber; a rotary valve being provided between the liquid-chemical pipes, the first cleaning liquid pipe, the second cleaning liquid pipe and the processing chamber; a pump for increasing and reducing an inner pressure of the processing chamber; and a control unit controlling the rotary valve and the pump so as to supply the respective cleaning liquids to the processing chamber and discharge the same from the processing chamber to clean the processing chamber, wherein the control unit controls the rotary valve and the pump so as to clean the processing chamber, in which the paraffin infiltration treatment has been performed, with the xylene cleaning liquid stored in the second cleaning liquid reservoir, and the control unit 38 controls the rotary valve 30 and the pump 34 so as to clean the processing chamber 12, whose interior has been cleaned with the xylene cleaning liquid stored in the second cleaning liquid reservoir 21, with the ethanol cleaning liquid stored in the first cleaning liquid reservoir 19. the processing chamber for containing the tissue specimen; a plurality of liquid-chemical reservoirs (14, 16, 18) being connected to the processing chamber by liquid-chemical pipes, the liquid-chemical reservoirs (14, 16, 18) storing the liquid chemicals to be used for infiltration-treating the tissue specimen contained in the processing chamber, the liquid chemicals being ethanol, xylene and paraffin, each at different concentrations; characterized in that the apparatus includes a first cleaning liquid reservoir being connected to the processing chamber by a first cleaning liquid pipe, the first cleaning liquid reservoir storing ethanol which cannot be used for the infiltration treatment of the tissue specimen as an ethanol cleaning liquid; a second cleaning liquid reservoir being connected to the processing chamber by a second cleaning liquid pipe, the second cleaning liquid reservoir storing xylene which cannot be used for the infiltration treatment of the tissue specimen as a xylene cleaning liquid; a supply/discharge port for supplying liquid chemical to and discharging the same from the processing chamber; a rotary valve being provided between the liquid-chemical pipes, the first cleaning liquid pipe, the second cleaning liquid pipe and the processing chamber; a pump for increasing and reducing an inner pressure of the processing chamber; and a control unit controlling the rotary valve and the pump so as to supply the respective cleaning liquids to the processing chamber and discharge the same from the processing chamber to clean the processing chamber, wherein the control unit controls the rotary valve and the pump so as to clean the processing chamber, in which the paraffin infiltration treatment has been performed, with the xylene cleaning liquid stored in the second cleaning liquid reservoir, and the control unit 38 controls the rotary valve 30 and the pump 34 so as to clean the processing chamber 12, whose interior has been cleaned with the xylene cleaning liquid stored in the second cleaning liquid reservoir 21, with the ethanol cleaning liquid stored in the first cleaning liquid reservoir 19.