Fixing device and image forming apparatus

A fixing device comprising:

• a fixing belt configured to heat a sheet;
• a heater holding member which circulatably guides the fixing belt and holds a heater that heats the fixing belt;
• and
• a stay sheet metal which reinforces the heater holding member, wherein
• the heater holding member has:
• a base plate on which the stay sheet metal is placed;
• and
• a side wall erected on either side of the base plate in a short direction thereof,
• a pocket which keeps the stay sheet metal is formed in each side wall,
• the stay sheet metal has:
• a top plate;
• and
• a side plate bending and extending from either edge of the top plate in a short direction thereof, and
• a slit is formed in each side plate such that the side plates are kept in the pockets of the heater holding member.