Burner comprising: a supporting body which comprises a first tubular element and a second tubular element arranged inside the first tubular element itself, where the volume positioned between said first and said second tubular elements (2a, 2b) defines at least a first duct for the flow of a combustive fluid and where said second tubular element defines at least a second duct for the flow of a combustion fluid; said second tubular element comprising a union element defining an extremity section of said second duct; a combustion head associated with said supporting body and comprising diffusing means, communicating with said first duct and having a plurality of openings for the flow of the combustive fluid towards a combustion area, where said diffusing means comprise at least two diffusing elements (9a, 9b, 9c) having relative openings for the flow of the combustive fluid and mobile reciprocally the one to the other to change the relative position of said openings, and dispensing means of the combustion fluid, communicating with said second duct and having a plurality of gaps for the flow of the combustion fluid itself towards said combustion area; wherein said diffusing elements (9a, 9b, 9c) are fitted around said union element, wherein each of them has a plurality of said openings defined by respective through cuts extending along a portion of the relative diffusing element (9a, 9b, 9c), where said openings have a substantially curvilinear extension and have a growing section proceeding outwards, and wherein said union element has at least a section which diverges proceeding towards said diffusing elements (9a, 9b, 9c), where said diverging section protrudes inside said first duct and is suitable for directing the combustive fluid flow towards the outer portions of said openings. a supporting body which comprises a first tubular element and a second tubular element arranged inside the first tubular element itself, where the volume positioned between said first and said second tubular elements (2a, 2b) defines at least a first duct for the flow of a combustive fluid and where said second tubular element defines at least a second duct for the flow of a combustion fluid; said second tubular element comprising a union element defining an extremity section of said second duct; a combustion head associated with said supporting body and comprising diffusing means, communicating with said first duct and having a plurality of openings for the flow of the combustive fluid towards a combustion area, where said diffusing means comprise at least two diffusing elements (9a, 9b, 9c) having relative openings for the flow of the combustive fluid and mobile reciprocally the one to the other to change the relative position of said openings, and dispensing means of the combustion fluid, communicating with said second duct and having a plurality of gaps for the flow of the combustion fluid itself towards said combustion area; wherein said diffusing elements (9a, 9b, 9c) are fitted around said union element, wherein each of them has a plurality of said openings defined by respective through cuts extending along a portion of the relative diffusing element (9a, 9b, 9c), where said openings have a substantially curvilinear extension and have a growing section proceeding outwards, and wherein said union element has at least a section which diverges proceeding towards said diffusing elements (9a, 9b, 9c), where said diverging section protrudes inside said first duct and is suitable for directing the combustive fluid flow towards the outer portions of said openings.