To provide a redundancy type measuring liquid residual quantity measuring device capable of improving failure resistance by removing a switch means and a switch control part, and thereby improving reliability as a measuring device.

In a signal processing system 1 and a signal processing system 2 which are to be redundant, a constitution is adopted, wherein excitation signals Se1(f1), Se2(f2) having mutually different frequencies are superimposed and applied to a sensor part (capacitance type sensor) 3, and an output signal So acquired through a voltage conversion part (charge amplifier) 10 is introduced to operation parts 8-1, 8-2 through synchronous rectification parts 15-1, 15-2. The synchronous rectification parts 15-1, 15-2 rectify synchronously the output signal So from the voltage conversion part 10 respectively by the frequencies f1, f2.