A fixing device includes a first pressing member, a fixing belt, a second pressing member, a tensioning section on which the fixing belt is wound on an upstream side relative to the fixing nip in a rotation direction of the fixing belt and which is configured to impart tension to the fixing belt, and a control section configured to control the tensioning section such that the shape in an axial direction of the fixing belt is changed in accordance with a type of sheet which passes through the fixing nip.

A fixing device includes a first rotary body, a second rotary body to contact the first rotary body, and a plain bearing that supports the first rotary body or the second rotary body. One rotary body of the first rotary body and the second rotary body has an outer diameter increasing, while the other rotary body has an outer diameter decreasing, in a curved line from an axial center portion to axial end portions of the first rotary body and the second rotary body at least between the first rotary body and the second rotary body. A recording medium passes between the first rotary body and the second rotary body with a circumferential component of a shear force generated between the first rotary body and the second rotary body by use of the plain bearing being in a range of from 15N to 25N.

A semiconductive roller is provided, which includes a tubular main body having a multiplicity of concavities (2) provided in an outer peripheral surface (1) thereof in at least one of circumferentially overlapping relation and axially overlapping relation. The concavities are each gently concave toward a center thereof from an outer periphery thereof. A semiconductive roller production method is also provided, which includes the step of forming the concavities by a laser processing method.

A fixing device includes a first rotary body, a second rotary body to contact the first rotary body, and a plain bearing that supports the first rotary body or the second rotary body. One rotary body of the first rotary body and the second rotary body has an outer diameter increasing, while the other rotary body has an outer diameter decreasing, in a curved line from an axial center portion to axial end portions of the first rotary body and the second rotary body at least between the first rotary body and the second rotary body. A recording medium passes between the first rotary body and the second rotary body with a circumferential component of a shear force generated between the first rotary body and the second rotary body by use of the plain bearing being in a range of from 15N to 25N.