Gas burner of the type having a cup of the burner accommodating at least one injector for fuel gas, a head of the burner coupled to the cup and including at least one distribution chamber for a first circumferential flame spreader, a mixing chamber for mixing primary air and fuel gas to set up a fuel mixture, the mixing chamber being fluidically connected to the cup and an injector, a duct for transferring the fuel mixture from the mixing chamber into the distribution chamber, and inflow duct of the primary air from the outer environment inside the cup of the burner, as well as a separating element of the transferring duct of the fuel mixture from the inflow duct of the primary air, wherein the separating element could be tightly constrained to the head, or cup of the burner.