An operation device includes a screen display section that displays a login screen on a touch panel, a key position changing section, a key information reception section, and a key information determination section. The key position changing section changes positions of a plurality of keys that are displayed on the login screen such that the keys are displayed for a current login process at positions that are different from previous positions at which the keys were displayed for a previous login process. The key information reception section generates input information representing a key pressed on the login screen. The key information determination section allows login of a user when a combination of pieces of input information corresponding to a plurality of key presses performed by the user matches registration information and does not allow login of the user when the combination does not match registration information.