having a variable direction to inject the mixed flow into the furnace a secondary air nozzle for feeding combustion auxiliary air to around the primary air nozzle a pulverized fuel supply pipe for feeding the mixed flow to said primary air nozzle and a windbox receiving said pulverized fuel supply pipe therethrough for forming a combustion auxiliary air supply passage around the pulverized fuel supply pipe the windbox is constructed by arranging unit windboxes in a separated or jointed relation with respect to each other each unit windbox has at least one pulverized fuel supply pipe and one combustion auxiliary air supply passage a rich lean flow separator is disposed at or near a jointed portion between said primary air nozzle and said pulverized fuel supply pipe the rich lean flow separator is able to change its direction in response to or independently of a change in an injection direction of the primary air nozzle as a result the rich lean flow separator varies following the change in the injection direction of the primary air nozzle so that the mixed flow can be injected as a reliable and stable flow without any biasing in the direction of the primary air nozzle from the primary air nozzle into the furnace thereby providing a highly reliable pulverized fuel combustion burner the pulverized fuel combustion burner according to the invention to further comprises another rich lean air separator disposed upstream of the first named rich lean flow separator as a result the flow separation is made at first by the rich lean flow separator upstream the mixed flow can be guided.