PURPOSE: To obtain a liquid-level detector being compact and having improved accuracy and reliability by optically connecting a light-emitting element and a photoactive element which are connected together through conductors on a wiring board, with a pair of optical fibers having one end formed into a total reflection face, and installing this in a given container together with conductors to the elements.

CONSTITUTION: Lead wires 29W32 of a light-emitting element 21 and a photoactive element 22 are connected to conductors 33W35 through a wiring board 24. A pair of optical fibers 27a and 27b having a junction portion 28a whose one end 28 is a total reflection face are contacted with the light-emitting element 21 and the photoactive element 22 through a holding member 25 and a supporting member 26, and optically connected. The detector is inserted into, e.g., a container 42 monolithicly provided to a discharge port 41a of a discharge portion 41 of an electrically-operated pump, and fixed. When the level of the liquid flowing in from a lower part 43 reaches the total reflection face 28b, light from the light-emitting element 21 is no longer applied to the photoactive element 22, so that the liquid level can be sensed. Thus, the detector being compact and having improved accuracy and reliability can be obtained.