PURPOSE:To detect the shortage of engine lubricating oil from the change in the resistance of a thermistor, by providing the thermistor so that it is in contact with the engine lubricating oil sprinkled in a crankcase due to engine running. CONSTITUTION:When the amount of engine lubricating oil in a crankcase has become lower than a prescribed level, enough lubricating oil is not sprinkled in the crankcase. As a result, a first thermistor Th1 comes out of contact with enough lubricating oil so that the temperature of the thermistor rises and its resistance decreases. Then, a first transistor Tr1 is turned off and other transistors Tr2, Tr5, Tr4, Tr3 are also turned off in that order. Charge stored in a capacitor C4 is sent out to an output terminal (e) through the transistor Tr3 to drive an indicator to show that the amount of the engine lubricating oil has dropped below the prescribed level.