A lubricant metering device includes a cup-shaped body with a supply passage coupled to a valve element, a hollow tubular body with a free end facing the valve element, a piston slidingly sealed inside the cup-shaped body and along an external surface of the tubular body, an elastic element exerting a load on the piston towards the supply passage, delineating an accumulation chamber facing the valve element and a dispensing chamber in constant communication with the cavity of the tubular body, also in communication with a delivery passage, the valve element closing the free end of the tubular body, isolating the cavity from the accumulation chamber and allowing communication with the supply passage, or isolating the accumulation chamber from the supply passage and allowing communication with the cavity. A stop limits the piston stroke towards the elastic element to adjust the dispensing of lubricant.