To provide a liquid level detector of high safety by simple constitution.

A control part 14 compares a temperature of a heater 21 detected by a temperature detecting resistance 22 with a temperature of an engine oil detected by a thermistor 12, when electric power is not supplied from an electric power control part 13 to the heater 21. The heater 21 is not heated when the electric power is not supplied to the heater 21, and the temperature of the heater 21 is thereby near to the temperature of the engine oil. The control part 14 judges based thereon the generation of abnormality in the temperature detecting resistance 22 or the thermistor 12, when a prescribed temperature difference is generated between the heater 21 and the engine oil. The control part 14 stops based thereon the supply of the power supplied from the electric power control part 13 to the heater 21, so as to prevent the temperature of the heater 21 from being risen.