A secondary transfer device for secondary-transferring a toner image primary-transferred on an outer peripheral surface of an endless annular intermediate transfer belt to a sheet at a predetermined secondary transfer position, the intermediate transfer belt having a predetermined width and being wound around a plurality of rollers and rotating, the secondary transfer device comprising: a pressure-releasing mechanism that displaces a secondary transfer roller to a pressing position, where the intermediate transfer belt is interposed and pressed between the secondary transfer roller and an opposite roller that abuts an inner peripheral surface of the intermediate transfer belt at the secondary transfer position, and a separation position separated from the outer peripheral surface of the intermediate transfer belt; a first drive that drives the pressure-releasing mechanism; a high-speed depressurization mechanism that temporarily depressurizes a nip pressure, at which the secondary transfer roller at the pressing position interposes and presses the intermediate transfer belt in a gap with respect to the opposite roller, when a leading end and a tailing end of a sheet pass between the secondary transfer roller and the intermediate transfer belt; and a second drive that drives the high-speed depressurization mechanism, wherein the pressure-releasing mechanism and the high-speed depressurization mechanism are arranged such that projected images of the pressure-releasing mechanism and the high-speed depressurization mechanism when projected in an axial direction of the secondary transfer roller overlap, wherein the pressure-releasing mechanism includes a pressing cam that is supported to a rotation shaft driven by the first drive in the same direction as an axis of the secondary transfer roller, and a pressing arm that abuts on the pressing cam and swings to displace the secondary transfer roller to the pressing position and the separation position, the high-speed depressurization mechanism includes a depressurization cam that is supported to a rotation shaft driven by the second drive in the same direction as an axis of the secondary transfer roller, and a depressurization arm that abuts on the depressurization cam and swings to displace the axis of the secondary transfer roller in the pressing position in a direction in which the nip pressure decreases, and the projected images of the pressing cam and the depressurization cam overlap with each other, wherein a rotation fulcrum of the depressurization arm is located between a force point where the depressurization arm receives a force from the depressurization cam and a working point where the depressurization arm applies a force in a direction in which the nip pressure decreases. a pressure-releasing mechanism that displaces a secondary transfer roller to a pressing position, where the intermediate transfer belt is interposed and pressed between the secondary transfer roller and an opposite roller that abuts an inner peripheral surface of the intermediate transfer belt at the secondary transfer position, and a separation position separated from the outer peripheral surface of the intermediate transfer belt; a first drive that drives the pressure-releasing mechanism; a high-speed depressurization mechanism that temporarily depressurizes a nip pressure, at which the secondary transfer roller at the pressing position interposes and presses the intermediate transfer belt in a gap with respect to the opposite roller, when a leading end and a tailing end of a sheet pass between the secondary transfer roller and the intermediate transfer belt; and a second drive that drives the high-speed depressurization mechanism, wherein the pressure-releasing mechanism and the high-speed depressurization mechanism are arranged such that projected images of the pressure-releasing mechanism and the high-speed depressurization mechanism when projected in an axial direction of the secondary transfer roller overlap, wherein the pressure-releasing mechanism includes a pressing cam that is supported to a rotation shaft driven by the first drive in the same direction as an axis of the secondary transfer roller, and a pressing arm that abuts on the pressing cam and swings to displace the secondary transfer roller to the pressing position and the separation position, the high-speed depressurization mechanism includes a depressurization cam that is supported to a rotation shaft driven by the second drive in the same direction as an axis of the secondary transfer roller, and a depressurization arm that abuts on the depressurization cam and swings to displace the axis of the secondary transfer roller in the pressing position in a direction in which the nip pressure decreases, and the projected images of the pressing cam and the depressurization cam overlap with each other, wherein a rotation fulcrum of the depressurization arm is located between a force point where the depressurization arm receives a force from the depressurization cam and a working point where the depressurization arm applies a force in a direction in which the nip pressure decreases.