Provided is a liquid surface detection device providing for compactness and enabling a reduction in displacement of a rotating shaft of a magnet. In the liquid surface detection device, which is provided with a holder rotating in response to displacement of a float, said displacement accompanying a change in a liquid surface, which is provided with a magnet affixed to the holder and rotating along with the holder, and which is provided with a magnetic detection element detecting a magnetic force change accompanying the rotating motion of the magnet, said liquid surface detection device is provided with: a body section that provides on the holder, first and second rotating sections sandwiching the magnet therebetween in the rotary axis direction of the magnet, said body section being provided with a first rotary support section that places the magnetic detection element opposite the magnet in the rotary axis direction of the magnet, and that rotatably supports the first rotation section of the holder; and a cover that is affixed to the body section, and is provided with a second rotary support section that rotatably supports the second rotating section of the holder.