Abstract: A rapid rise in the temperature of a liquid level sensor is prevented even at close to a vacuum atmosphere. In a material supply system that is equipped with a tank containing a liquid material and with the liquid level sensor that is provided inside the tank, and in which the liquid level sensor is a self-heating type of sensor that, when the liquid level sensor is generating heat as a result of being supplied with a predetermined normal energy, detects a liquid surface, there are provided a monitoring portion that monitors a detection value from an output signal from the liquid level sensor, and an energy control portion that, when the monitored detection value reaches a predetermined upper limit value, performs control in such a way that the energy supplied to the liquid level sensor is low-level energy that is lower than the normal energy.