To provide a position detector for determining the position of a magnet, its moving direction, or whether passage takes place, by detecting the turning on/off of reed switches, without being affected by external vibration, etc., and to provide a liquid level sensor that uses the same.

The reed switches L11, L12 to L51, and L52, are disposed so that they form pairs with prescribed spaces left in between them in the moving direction of the magnet 3, while their positions are severally shifted from each other in the moving direction. Whether their respective contacts are closed is determined and which contacts are closed earlier is detected, thereby the moving direction of the magnet or whether movement takes place is determined. When the magnet 3 is moved vertically along a liquid surface with the reed switches L11, L12 to L51, and L52 disposed vertically, liquid level can be determined by means of the reed switches L11, L12 to L51, and L52.