PURPOSE: To provide a liquid level controller which can be suitably applied also to the oil level control of a flier by combining a controller with a weight sensor which detects the apparent weight of a weight that receives the liquid buoyancy and adding an empty weight correction circuit to the controller.

CONSTITUTION: A weight sensor LC consisting of a load cell, for example, is placed above a universal joint W1, measures the apparent weight w of the weight w which receives the buoyancy by the oil A, and outputs a detection signal S1. When the lever L of the oil A is low and the oil A does not reach the lower end of the weight w, the sensor LC detects the empty weight wo of the weight w as w=wo. When the level L rises and the weight w sinks in the oil A by depth Lf, the weight w receives the buoyancy wf and w=wo-wf is satisfied. The empty weight correction circuit of a controller 10 calculates the difference wo-(wo-wf)=wf between the weight w and the weight wo. In this instance, the buoyancy wf is proportional to the depth Lf of the weight w measured in the oil A and shows the level Lf of the oil A set on the basis of the lower end of the weight w.