A fixing device includes an endless belt, a backup roller, and a nip member having a first slide contact surface, a second slide contact surface, and a connecting surface connecting the first and second slide contact surfaces. A curvature radius of the second slide contact surface is greater than that of the backup roller in cross section perpendicular to an axis of the backup roller. The connecting surface is disposed between a first imaginary plane and a second imaginary plane, the first imaginary plane including an edge of the endless belt and extending perpendicularly to the axis of the backup roller, the second imaginary plane including an end of a maximum image area proximate to the edge of the endless belt and extending perpendicularly to the axis of the backup roller.