A dispensing device for fluid substances, including a pushbutton in which a chamber is provided housing a piston, the piston being loaded by an elastic mechanism to urge a front projecting appendix thereof into a dispensing hole for the substance, to hence sealedly close the hole, the pushbutton presenting a seat enabling a hollow stem to be coupled therethrough through which the pressurized substance is fed to the device. In the chamber there is housed an at least partially cylindrical member in an interior of which the piston slides, in the member there being provided at least one passageway opening to the front of the piston and communicating with a bore of the stem when the device is positioned on the pump.