A device suitable for dispensing a liquid substance, such as an ophthalmological substance, including a container; a dispenser for dispensing the substance and which includes a piston element, loaded by the pressure of the pressurized substance so as to adopt a standby position by default that prevents the preloading chamber from being flooded by a dose of the substance; and a valve element capable of enabling a connection between the preloading chamber and the outside. The device has an actuation mechanism that sequentially compresses a volume of air used for moving the piston element from the standby position thereof, allowing a dose of the substance to flood the preloading chamber to subsequently mechanically actuate the valve element and simultaneously enable the connection to the outside of the preloading chamber as well as of the volume of air previously used for moving the piston element from the standby position thereof.