To additionally set a means which detects the amount of a filled liquid remaining in a tank and generates an alarm when the amount of the remaining liquid is reduced to a predetermined value or water is mixed, etc.

A supporting body 1 inserted and arranged in a longitudinal attitude in a tank is provided with float guides 7, 8, 9. A main float is arranged to move up and down along the float guides. A coil spring is set to urge and press the main float 11 downward. The main float 11 would naturally move up or down with a stroke of a height H in accordance with a rise or fall of a liquid level before the amount of a remaining liquid approaches zero after the tank is fully filled. However, the stroke H is reduced and displayed as a stroke (h) from an F display to an E display at a display member 24 because of the coil spring 14. When the water is collected at a bottom part of the tank, a water detection float 16 rises and a reed switched installed inside the supporting body 1 generates a signal. When the amount of a remaining kerosene decreases to a predetermined value, a remaining amount detection float 20 descends and the reed switch generates a signal.