A sensing apparatus including: a first electrode member; a second electrode member arranged at opposing positions a predetermined distance away and electrically isolated from the first electrode member; and an electric circuit connected to the first and second electrode members. The first and the second electrode members are operatively connected by an impedance formed between the first and the second electrode members in response to existence of a substance to be sensed between the first and the second electrode members. The electric circuit outputs a signal in response to the impedance. The sensing apparatus is applicable for detecting, for example, the level of a liquid in a vessel.