The present invention relates to an operating device for a flush water tank device in a flush toilet wherein manual and motorized control units are configured to actuate a flush valve by means of a single connecting member operably connecting the manual and motorized control units to the flush valve. The operating device is characterized by a single connecting member operatively connected to the flush valve for opening and closing the flush valve depending on a pull-up amount of the connecting member, a manually operating unit for pulling up the single connecting member when a user performs a manual operation for the control unit, and an electrical drive unit adapted to pull up the single connecting member so as to actuate the flush valve by using an electrical power from an external power source.