To prevent temperature on the developing means side of a process cartridge from rising and to keep developer excellent so as to always form a normal image by providing an air course where air flows along the upper surface of the process cartridge.

When printing operation is started, the temperature in a device main body 37 rises due to heat generated by the heater 11a of a fixing means 11, and the temperature of the process cartridge B also begins to rise. A suction fan 29 provided in a manual paper feeding unit 28 sucks air outside the device, whose temperature is low, through a fan duct 30 and makes it blow through the hole 31a of a frame 31. Then the air whose temperature is low is made to blow into a dispersion chamber 50 in the space of a cartridge attaching part and dispersed in a longitudinal direction. The dispersed air flows in the air courses 51, 52 and 53, respectively. The air whose temperature is low and which is led to the air course 51 near by the cartridge attaching part descends along the bottom board 41b of the toner frame body 41 of the cartridge B so as to cool the toner frame body 41 of the cartridge B.