A liquid level detector 10 includes a liquid guiding pipe 14 that guides a liquid in a tank to an inside thereof in such a manner that a liquid level of the guided liquid conforms to a liquid level of the liquid in the tank, and a branching liquid guiding pipe 15 for detecting a liquid level, which branches off from the liquid guiding pipe to guide the liquid into an inside thereof in such a manner that a liquid level of the guided liquid conforms to a liquid level of the liquid in the tank. The branching liquid guiding pipe 15 is provided with position sensors 16 (16a, 16b, 16c, 16d) for detecting the liquid level of the liquid in the branching liquid guiding pipe 15. On a part where the liquid guiding pipe 14 and the branching liquid guiding pipe 15 are connected to each other, there is disposed a bubble passage prevention member 17 of a porous plate shape, which prevents bubble generated in the liquid from entering the branching liquid guiding pipe 15.