PURPOSE: The culture tank in the culture plate on the microscope is perfused sterilely with the culture mixture which is heated at a constant temperature to keep the tank itself at a constant temperature and enable the tank to be held in the same view.

CONSTITUTION: In arm 12, the tube for introducing the culture mixture is wound with heater coil 2 and connected to the thermistor 3. The inlet nozzle 5 is connected to the tank 3 so that the top end comes into the culture tank 16. Simultaneously, exhausting nozzle 6 is connected from the culture tank 6 to the pipe 10. The thermistor probe 26 in the thermistor tank 3 is connected through the thermistor tank cap 4 to the thermistor 22 provided with a constant- current unit 23. Further, the inlet tube 1 and the exhaust tube 10 are connected to the reservoir bottle for perfusion solution 25 and either the inlet tube 1 or the exhausting tube is equipped with a peristaltic pump 21. As a result, the culture tank itself is always kept at a constant temperature.