To detect the liquid level surely through a simple structure by disposing a float part, moving up and down depending on the liquid level, along the axis of a switch section disposed in the direction intersecting the liquid level in a tank thereby decreasing the number of components.

A liquid lever sensor 10 formed into substantially tubular shape is disposed in the direction intersecting the level of gasoline in a gasoline tank. A float part 28 is disposed in a washboard part 26 fitted to the forward end at the lower part of body section 30 while being fitted idly to the top part 30a thereof. When gasoline flows into the washboard part 26 through a slit 26c made in the side face at the upper edge 26a thereof, the float part 28 moves up and down within a predetermined range depending on the level change of gasoline to switch a lead relay 32a at the forward end of switch section (detecting section) 32 through a magnet 28b. Consequently, residual quantity of gasoline (liquid level) can be detected and indicated by combining the on/off state of relay 32a with the driving state of engine.