Fixing device and image forming apparatus capable of effectively suppressing thermal energy released externally from device due to thermal convection and hot air flow

An image forming apparatus comprising:

• image forming means for forming a toner image;
• and
• a fixing device for fixing said toner image onto a recording paper, wherein
• said fixing device includes:
• a heating member for heating said recording paper,
• a pressing member for pressing said heating member by pressure-applying contact,
• a casing accommodating said heating member and said pressing member, and being provided with an exit port for discharging said recording paper, and
• a closing unit added to said exit port for keeping a temperature of said casing;
• and
• said closing unit has:
• a rotation member, and
• an opposed member forming a nip region together with said rotation member.