A burner 15 where a secondary air regulator 36 is provided on a forward end of a nozzle main unit 16 to be installed along the central axis of a burner throat 13 being installed on a furnace wall 12 and to be accommodated in a wind box 14, wherein the secondary air regulator has an end plate 37 having a bored hole 38 penetrating in an axial direction and for forming a cylindrical space 48 with peripheral surface opened in a space with the furnace core side surface of the wind box, a rotary damper 42 having a bored hole 45 penetrating in an axial direction and being capable to open or close the hole on the end plate by rotating in a peripheral direction, a sliding damper 52 for surrounding the cylindrical space and being slidable in an axial direction, air vanes 46 and 47 installed at a predetermined distance along circumference of the cylindrical space and for giving swirling to the secondary air 34, first driving means 54, 56 and 44 for rotating the rotary sliding damper, and second driving means 53 and 55 for sliding the sliding damper.