PURPOSE: To simplify the constitution and increase the reliability of the liquid level meter by measuring the liquid level based on the propagation time of the ultrasonic wave propagating in the magnetic distortion line.

CONSTITUTION: With output of the exciting pulse with fixed cycle from exciting pulse generator OS, current i2 flows to support part 2 via power transmission transformer 6. Current i2 then flows to magnetic distortion line 1. As a result, current i3 flows to secondary coil 32 of transformer 30 which shifts up and down along with float 3. Current i3 flows to exciting coil 40 in the form of the exciting pulse signal to generate the ultrasonic signal at line 1. At the same time, the exciting pulse given from generator OS sets the FF. With application of the exciting pulse to transformer 6, the ultrasonic signal is produced to line 1 at the position of coil 40 and propagates the line 1 to be received at reception means 5. Signal e obtained through means 5 resets the FF. As a result, the pulse featuring the time duration from set to reset is delivered from the FF. and the time of this pulse period is counted by counter CU.