A bone cement injecting tool is configured to be capable of inhibiting or preventing the occurrence of air bubbles in the liquid as a pressure transmitting medium. The bone cement injecting tool is composed of a first cylinder possessing a bore, a second cylinder possessing a bore, a first gasket slidably sealing the bore of the first cylinder, a second gasket slidably sealing the bore of the second cylinder, a tube communicating the first cylinder and the second cylinder, and liquid (e.g., water) filling the space I the tube and the first and second cylinders between the two gaskets. A piston is positioned in the first cylinder, and a pressure-retaining member applies pressure to the forward end of the piston so the piston moves the first gasket toward the forward end, thereby delivering the water to the second cylinder through the tube. During storage, the pressure-retaining member pushes the piston toward the fore-end, and this pushing force produces the pressure of the water.