Abstract: A means receiving a light returning from an optical recording medium and detecting the beam distribution in the tangential direction of the track of the recording medium is provided. The offset of at least one controlling signal of a focusing controlling signal and tracking controlling signal is eliminated by the output signal of this beam distribution detecting means.

Abstract: A flowcell for containing sample solutions is surrounded by an electric heater which is then surrounded by an isothermal frame having a large heat capacity, and a Peltier element serving as a cooling source is coupled with the isothermal frame. A heat delaying plate is arranged between the flowcell and heater and a temperature sensor is arranged between the flowcell and the heat delaying plate. The Peltier element is controlled in such a manner that the temperature of the isothermal frame is maintained substantially at a constant temperature lower than a predetermined temperature at which the sample solution is to be kept. The heater is controlled in accordance with a difference between the temperature of the sample solution and the predetermined temperature.