A liquid level detector (1) used for water level control for a boiler. An inner tube (31) is mounted in an outer tube (30) so as to vertically penetrate therethrough. An electrode rod (36) is inserted into the outer tube (30) so as to be located outside the inner tube (31). The inner tube (31) is connected at the upper end thereof to an upper header via a gas phase-side communication tube and at the lower part thereof to a lower header via a liquid phase-side communication tube. At the upper and lower portions in the outer tube (30), there are communication holes (34, 35) formed in the peripheral side wall of the inner tube (31). The upper communication hole (34) is formed at a position not facing the electrode rod (36). This prevents vapor from the upper header and water entrained in the vapor from directly making contact with the electrode rod (36), and as a result, erroneous water level detection is prevented.
