The present invention relates to a system for detecting the remaining amount of liquid in a tank, which is suitably used, for example, in detecting the remaining amount of fuel accumulated in an automotive fuel tank. 
Typically, as disclosed in JP-U 64-38534, the fuel tank mounted on the vehicle is provided with a float-type level detecting system, for example, to detect the remaining amount of fuel accumulated in the tank.  The float-type level detecting system comprises essentially a float arranged vertically movably with the level of fuel accumulated in the fuel tank, a sensor part fixedly arranged in the tank and for sensing a fuel level position in accordance with displacement of the float, and a displacement transmitting part comprising an arm for transmitting displacement of the float to the sensor part. 
When fuel in the fuel tank increases or decreases, the float moves vertically with the fuel level, which is transmitted to the sensor part where the fuel remaining amount in the tank is detected in accordance with a fuel level position. 
However, the typical level detecting system is constructed to detect the fuel remaining amount through the sensor part fixedly mounted to the top face of the fuel tank, to which displacement of the float moving vertically with the level of fuel in the fuel tank is directly transmitted through the arm.  Such construction causes the following problem. 
In recent passenger cars and the like, there is a tendency to make fuel tanks from a light flexible material such as synthetic resin so as to achieve a weight reduction in the whole car.  The fuel tanks made from a light flexible material can be deformed with variations in weight of fuel accumulated therein, tank pressure, and ambient temperature, and with vibrations, impact, and the like occurring during vehicle cruising. 
When the fuel tank is deformed, the level of fuel in the fuel tank is displaced vertically accordingly.  Then, the above level detecting system detects and outputs the fuel remaining amount including this level displacement as variations in the fuel remaining amount, which is different from the actual fuel remaining amount, leading to impossibility of stable detection of the correct fuel remaining amount.