An opening/closing apparatus includes: an apparatus body; a pivot body pivotable between a close position covering an upper portion of the apparatus body and an open position releasing the upper portion of the apparatus body; a rack member provided on the pivot body and having a rack gear extending in a radial direction from a pivot base end portion to a pivot front-end portion of the pivot body; and an arm body having one end portion connected to the apparatus body and the other end portion connected to the rack member and slidably movable relative to the rack member. The arm body includes: a housing; a rotary damper supported by the housing and having a damping gear receiving damping force from viscous fluid; and a gear section supported by the housing and transmitting the damping force of the damping gear to the rack gear.