A liquid level measuring apparatus comprising: ultrasonic sensors each configured to transmit and receive an ultrasonic wave, the ultrasonic sensors being respectively set at a plurality of positions on an outer surface of a container that can store at least one of a liquid or a gas; a transmission/reception controlling unit configured to set, as a target, any one of the ultrasonic sensors at the plurality of positions and control the transmission and reception of the ultrasonic wave of the target; an intensity detecting unit configured to detect an intensity of the ultrasonic wave that satisfies at least 2 ≤ N (N: natural number), of the ultrasonic waves that are reflected N times on an inner surface of the container; a gas/liquid determining unit configured to determine which of the liquid and the gas a reflection point on the inner surface is in contact with, on a basis of the detected intensity of the ultrasonic wave; and a level determining unit configured to determine a liquid level of the liquid on a basis of gas/liquid determination results respectively derived by the ultrasonic sensors at the plurality of positions; characterized by a pulse train generating unit configured to generate the ultrasonic wave made of a plurality of pulse trains with a set number of continuous waves p, wherein the transmission/reception controlling unit is configured to cause each of the ultrasonic sensors to transmit the ultrasonic wave made of the pulse trains, and the gas/liquid determining unit is configured to calculate an average value of respective intensities of pulses having the number of continuous waves p. ultrasonic sensors each configured to transmit and receive an ultrasonic wave, the ultrasonic sensors being respectively set at a plurality of positions on an outer surface of a container that can store at least one of a liquid or a gas; a transmission/reception controlling unit configured to set, as a target, any one of the ultrasonic sensors at the plurality of positions and control the transmission and reception of the ultrasonic wave of the target; an intensity detecting unit configured to detect an intensity of the ultrasonic wave that satisfies at least 2 ≤ N (N: natural number), of the ultrasonic waves that are reflected N times on an inner surface of the container; a gas/liquid determining unit configured to determine which of the liquid and the gas a reflection point on the inner surface is in contact with, on a basis of the detected intensity of the ultrasonic wave; and a level determining unit configured to determine a liquid level of the liquid on a basis of gas/liquid determination results respectively derived by the ultrasonic sensors at the plurality of positions; characterized by a pulse train generating unit configured to generate the ultrasonic wave made of a plurality of pulse trains with a set number of continuous waves p, wherein the transmission/reception controlling unit is configured to cause each of the ultrasonic sensors to transmit the ultrasonic wave made of the pulse trains, and the gas/liquid determining unit is configured to calculate an average value of respective intensities of pulses having the number of continuous waves p.