<p>Provided is a tissue piece treating apparatus comprising an automatic controlling means for feeding back the temperature of the treatment liquid (5) or molten paraffin (5') in the bath inside (2) detected by a temperature sensor (S) to switch a heating mode and a cooling mode alternately to control the temperature; a heating means for turning OFF in an air-cooling fan (F) of the ultrasonic vibrator (6) and ON in a plane heater (H) at the heating mode, thereby transferring the heat generated by the ultrasonic vibrator (6) and the plane heater (H); and, a cooling means for turning ON in the air-cooling fan (F) of the ultrasonic vibrator (6) and OFF in the plane heater (H) at the cooling mode, thereby blocking the heat transfer from the ultrasonic vibrator (6) and the plane heater (H) to the bath inside (2). These means can suppress the excessive heating of a tissue piece (3) so that they can suppress the heating modification of the tissue piece (3).</p>
