A fixing unit comprising: a fixing roller; a pressure roller configured to form a fixing nip portion by engaging with said fixing roller under pressure; an air nozzle located near said fixing nip portion in the paper discharge side of said fixing nip portion to blow paper separating air toward the leading edge of a sheet which is passed through said fixing nip portion, wherein said pressure roller is able to move into and out of engagement with said fixing roller as engagement/disengagement motion, and wherein the nozzle tip of said air nozzle is able to move between an operating position near said fixing nip portion and a parking position to which the nozzle tip is retracted from the operating position in synchronization with the engagement/disengagement motion of said pressure roller; and a guide mechanism configured to guide the motion of said nozzle tip between said operating position and said parking position, said guide mechanism comprising: a nozzle support pin which laterally protrudes from a side of said air nozzle in a length direction of said air nozzle; and a guide member provided on a free end of an arm member performing the engagement/disengagement motion of said pressure roller, and configured to guide said nozzle support pin to said operating position by supporting said nozzle support pin at least in a position enabling engagement between said pressure roller and said fixing roller under pressure. a fixing roller; a pressure roller configured to form a fixing nip portion by engaging with said fixing roller under pressure; an air nozzle located near said fixing nip portion in the paper discharge side of said fixing nip portion to blow paper separating air toward the leading edge of a sheet which is passed through said fixing nip portion, wherein said pressure roller is able to move into and out of engagement with said fixing roller as engagement/disengagement motion, and wherein the nozzle tip of said air nozzle is able to move between an operating position near said fixing nip portion and a parking position to which the nozzle tip is retracted from the operating position in synchronization with the engagement/disengagement motion of said pressure roller; and a guide mechanism configured to guide the motion of said nozzle tip between said operating position and said parking position, said guide mechanism comprising: a nozzle support pin which laterally protrudes from a side of said air nozzle in a length direction of said air nozzle; and a guide member provided on a free end of an arm member performing the engagement/disengagement motion of said pressure roller, and configured to guide said nozzle support pin to said operating position by supporting said nozzle support pin at least in a position enabling engagement between said pressure roller and said fixing roller under pressure. a nozzle support pin which laterally protrudes from a side of said air nozzle in a length direction of said air nozzle; and a guide member provided on a free end of an arm member performing the engagement/disengagement motion of said pressure roller, and configured to guide said nozzle support pin to said operating position by supporting said nozzle support pin at least in a position enabling engagement between said pressure roller and said fixing roller under pressure.