1. A processing execution apparatus having a processing program defined in segments for executing a predetermined function by performing interrupt processing between execution unit programs, each of the execution unit programs includes a data update program which updates a series of data requiring simultaneousness of referencing when a data update request is made, wherein the processing program has: an update management program which notifies the data update program of the update request and moves to an update status, and determines completion of update of the series of data by the data update program, by an update completion notification from the data update program, and moves to a standby status; and a reference limiting program which inhibits another program from referring to the series of data if the update management program is in the update status.