To provide a precise liquid level indicator that can be manufactured inexpensively since it does not cause a light reflector to be contaminated by solution, or the like, is capable of measurement stably with less maintenance, does not cause a phenomenon, such as ignition, from occurring by the electrical circuit, or the like in a measurement system, and also can be configured by a simple electrical circuit.

The liquid level indicator has a means having a reflecting plate in a cylinder airtightly separated from liquid to be measured and moving the reflecting plate to a liquid level position by a magnet mounted to a float floating on the surface of the liquid. The height of the liquid level is determined by measuring the reflection delay time of light. A relaxation oscillator in which a frequency is determined by delay time is composed for the measurement, and the frequency is measured, thus obtaining the economical liquid level indicator.