To provide a water amount detecting device attached to a water meter and provided with a reading part for reading a display part and a control part for detecting and transferring a water amount from output of the reading part, in which water is prevented from being splashed onto the reading part and the control part which are principal parts of the water amount detecting device, when there is inundation in the water meter.

A water amount detecting device is additionally attached to a water meter 70 to be housed in a water meter box 90. The water amount detecting device comprises: a reading part 11 for reading a display part 71 of the water meter 70; and a control part 12 for detecting a water amount from output of the reading part 11. The control part 12 transmits the water amount, and the reading part 11 and the control part 12 are housed between a cover 90a of the water meter box 90 and the display part 71.