To stably and sensitively provide a device for detecting an object such as liquid level regardless of the property of the object.

The device 10 for detecting the liquid level in a liquid tank comprises: a pipe 1 that has one or two openings at and/or near a first end and where the opening varies according to the liquid level when the first end is arranged in the liquid tank; a flowmeter 4 capable of measuring the flow rate of gas in the pipe 1; and a means 5 for sucking or sending air to a second end of the pipe. The pipe 1 has a release port 6 between the first end and the second end.