Abstract: A programmable display device includes a state monitoring section for monitoring a state of a preregistered variable. Data of an image to be displayed by the programmable display device contains (i) a plurality of unit objects and (ii) a master object that collectively controls the plurality of unit objects. The master object has a change determining section and a display switching section. The change determining section notifies the display switching section that the preregistered variable monitored by the state monitoring section has been changed so as to be in a state within a particular range. Upon receipt of the notification, the display switching section switches one of the plurality of unit objects, which are being displayed, with another unit object, and then displays the another unit object.