A fuser has a heater, a heat roller, an endless belt, a pressure pad, and a slidable sheet. The pressure pad forms a nipping portion to nip the endless belt between the pressure pad and the heat roller. The slidable sheet is interposed between an inner circumferential surface of the endless belt and the pressure pad in the nipping portion. The slidable sheet includes a plurality of dents and a plurality of projections on a surface contacting the inner circumferential surface of the endless belt. The plurality of dents are arranged in a first part of the surface of the slidable sheet. The first part is located in a range corresponding to the nipping portion. The plurality of projections are arranged in a second part of the surface of the slidable sheet. The second part is located in a range corresponding to a portion different from the nipping portion.

In a fixing device, a first fixing member and a second fixing member are configured to form a nip in combination, and an arm biased by a first spring with a first biasing force provides a nip pressure. A cam rotatably arranged to cause the arm to move against the first biasing force has a first cam surface used to change the nip pressure from a first pressure to a second pressure smaller than the first pressure, and a second cam surface of which an angle of action is greater than that of the first cam surface to change the nip pressure from the second pressure to a third pressure smaller than the second pressure. A maximum pressure angle at the second cam surface is smaller than a maximum pressure angle at the first cam surface.

A contact-separation device brings a contact-separation member into contact with a contacted member separably and includes a biasing member that generates a biasing force. A presser presses the contact-separation member against the contacted member in a pressing direction with the biasing force from the biasing member. A cam presses the presser in an opposite direction being opposite to the pressing direction. The cam is rotatable and has a cam face. A cam follower has a cam contact face that contacts the cam face of the cam. The cam contact face is curved to project toward the cam. The cam contact face has a curvature that is smaller than a greatest curvature of the cam face of the cam and is greater than a smallest curvature of the cam face of the cam.

An endless belt includes a base material layer containing a polymer material and conductive particles, wherein, in an image obtained by observing a cross section taken along a thickness direction of the base material layer with an atomic force microscope, a proportion of a total area Ap of cross sections of all the conductive particles is 9.0% or more and 14.5% or less with respect to a total cross-sectional area At of the base material layer, and a proportion of a total area Ab of cross sections of conductive particles having an area of 0.01 μm.sup.2 or more among cross sections of the conductive particles is 28.0% or more and 65.0% or less with respect to the total area Ap of cross sections of all the conductive particles.

A release sheet includes a support member including a positioning portion formed on a part, in a first direction along a longitudinal direction of the fixing belt, of the support member and configured to position the support member to a holding portion, that holds the fixing belt, in a second direction orthogonal to the first direction, and a release member fixed with the support member and including a front end portion that faces a surface of the fixing belt through a gap. One member among the support member and the release member includes an opening which is oblong in the second direction more than the first direction in order to adjust a distance between the front end portion and the positioning portion in the second direction.

In a fixing device, a first fixing member and a second fixing member are configured to form a nip in combination, and an arm biased by a first spring with a first biasing force provides a nip pressure. A cam rotatably arranged to cause the arm to move against the first biasing force has a first cam surface used to change the nip pressure from a first pressure to a second pressure smaller than the first pressure, and a second cam surface of which an angle of action is greater than that of the first cam surface to change the nip pressure from the second pressure to a third pressure smaller than the second pressure. A maximum pressure angle at the second cam surface is smaller than a maximum pressure angle at the first cam surface.

In a fixing device, a pressure unit is pressed toward a roller by an arm, to form a nip region. The pressure unit includes a belt configured to contact the roller in a nip region, a pressure pad configured to press the belt in combination with the roller, and a side guide including an end guide surface configured to guide a side end of the belt, and a stay configured to support the pressure pad. A supporting member is located on an outer side of the side guide that is opposite to an inner side on which the end guide surface faces. The supporting member is held between the stay and the arm, the supporting member comprising a contact surface which contacts the side guide and on which the side guide is swayably supported.

In an image forming device, a first fixing member has a roller. A second fixing member has a belt to form a nip together with the first fixing member. A first motor drives the roller. A pressure modifying mechanism modifies a nip pressure at the nip to selected one of a first nip pressure and a second nip pressure smaller than the first nip pressure. A controller starts driving the first motor to drive the roller in a case where a print command is received in a state that the nip pressure is the second nip pressure. The controller modifies the nip pressure from the second nip pressure to the first nip pressure after the driving is performed and fixes the developer image on the sheet in a state that the nip pressure is the first nip pressure.

A fixing device includes a fixing belt stretched taut around a plurality of supports, a pressure rotator to form a fixing nip between the fixing belt and the pressure rotator, a belt polishing mechanism to polish the fixing belt. The belt polishing mechanism includes a polishing roller to separably contact the fixing belt and slide over the surface of the fixing belt when the polishing roller is pressed against the fixing belt, a contact and separation driver to press and separate the polishing roller to and from the fixing belt, an opposed member disposed opposite the polishing roller via the fixing belt and configured to form a polishing nip with the fixing belt, and a polishing roller rotation mechanism to rotate the polishing roller. The polishing roller rotation mechanism includes a first rotator disposed coaxially with the polishing roller and a second rotator disposed coaxially with the opposed member.

A heating device includes a rotator, an opposed rotator configured to contact the rotator to form a nip, a heater configured to heat the rotator, and a plurality of pressing devices. The heater includes a first portion and a second portion. The second portion of the heater generates a larger amount of heat than the first portion of the heater. The pressing devices are arranged in a longitudinal direction of the heater and each configured to press at least one of the rotator and the opposed rotator and cause the rotator and the opposed rotator to press each other. The pressing devices include a first pressing device corresponding to the first portion of the heater and a second pressing device corresponding to the second portion of the heater, and the first pressing device generates a smaller pressing force than the second pressing device.