Abstract: A liquid circulation system includes a tank, a processing device, a first pump, a second pump, a liquid level sensor, and an adjuster. The tank is for storing a liquid. The processing device is for processing a subject using the liquid. The first pump is for feeding the liquid in the tank to the processing device. The second pump is for feeding the liquid used in the processing device to the tank. The liquid level sensor is for detecting a liquid level of the liquid in the tank below a threshold. The adjuster is for lifting the tank and adjusting a position of a surface of the liquid relative to the liquid level sensor to maintain the surface of the liquid above the liquid level sensor when an amount of the liquid in the tank is reduced.