Provided is a method for operating a pulverized coal-fired boiler facility, wherein upgraded low-grade coal can be safely used as fuel and an existing facility needs little remodeling. The present invention relates to a method for operating a pulverized coal-fired boiler facility (100) that uses upgraded brown coal as fuel. Boiler exhaust gas taken out of an exhaust gas duct (31) is added to air from a primary air fan (10) to prepare mixed gas with an oxygen concentration of less than 12% in a volume ratio, the mixed gas is caused to separately flow to a carrier gas duct (33) that goes through a GAH (8) and a bypass carrier gas duct (34) that bypasses the GAH (8), and thereafter the mixed gas is supplied to a mill (21).