Fixing device with endless belt and image forming apparatus incorporating same

A fixing device comprising:

• an endless belt rotatable in a predetermined direction of rotation;
• a nip formation assembly disposed opposite an inner circumferential surface of the endless belt;
• and
• an opposed rotary body pressed against a part of the nip formation assembly via the endless belt to form a fixing nip between the endless belt and the opposed rotary body through which a recording medium bearing a toner image is conveyed,
• the nip formation assembly including:
• a base pad defining the fixing nip and including:
• a pressure portion pressing against the opposed rotary body via the endless belt;
• an extension portion contiguous to and disposed upstream from the pressure portion in a recording medium conveyance direction, the extension portion not pressing against the opposed rotary body via the endless belt and over which the endless belt slides;
• and
• a curved portion disposed upstream from the extension portion in the recording medium conveyance direction and smoothly blending into the extension portion, the curved portion not pressing against the opposed rotary body.