A processing execution apparatus has an update management program and a reference limiting program. The update management program manages whether or not A- to C-data update programs are performing data update, and shows an update status indicating that update is being performed or a standby status indicating that update is not being performed. Then, the reference limiting program refers to the status of the update management program. If it is in the update status, the program does not notify an X-program including data reference processing of the received event. That is, execution of the X-program is controlled by notification/non-notification of the event. However, regarding a Y-program not including data reference processing, it directly operates in accordance with event.