Fixing device and image forming apparatus

A fixing device comprising:

• an endless belt member;
• a secured member disposed in a secured state to contact an inner peripheral surface of the belt member;
• a support roller that rotatably supports the belt member;
• a heating unit that heats the belt member;
• and
• a rotary pressurizing roller that includes an elastic surface layer that is elastically deformed when the belt member is pressed against the secured member to form a fixing part,
• wherein the secured member includes
• a recessed part provided on a surface of the secured member that faces the pressurizing roller and configured to curve the belt member along the secured member into a recessed shape in which the belt member is recessed from the pressurizing roller toward the secured member,
• projecting parts provided upstream and downstream of the recessed part, respectively, along a moving direction of the belt member and configured to curve the belt member into a projected shape in which the belt member is projected toward the pressurizing roller, and
• a region provided between at least one of the projecting parts provided upstream and downstream of the recessed part and the recessed part, the region having a small curvature compared to the corresponding projecting part.