To provide a water fire extinguisher function type bathtub water saving device, disposed in a bathtub in each home without any obstacle to bathing, saving the quantity of water filling the bathtub, and using the saved water for fire extinguishing at the initial stage of a fire.

This water fire extinguisher function type bathtub water saving device 5 is disposed in the bathtub 4 to save the quantity of water for the volume of the water saving device 5, and the water enclosed in the water extinguisher function type bathtub water saving device 5 is utilized as fire extinguishing water of a manual pressure type fire extinguisher.