To provide a level sensor capable of effectively knowing the residual quantity of liquid of a container, the liquid container and a liquid quantity detecting method.

The level sensor 18 has a monitoring unit 23 connected to sensor probes 20a, 20b arranged in the liquid container 4. The monitoring unit 23 has a probe potential difference detection part 25 detecting the output potential difference of the sensor probes 20a, 20b, a level discrimination part 26 discriminating the level of liquid from the detected result, and a liquid use quantity calculation part 27 counting the number of times of the bubbling period of bubbling gas from the detected result of the probe potential difference detection part 25 and calculating the use quantity and the residual quantity of liquid in the liquid container 4 from the number of times of the bubbling period and liquid use quantity data per unit bubbling period previously stored.