A processing apparatus which is capable of releasing priority use of apparatuses that are reserved for priority use but are not actually used, even when a plurality of apparatuses are used by priority during a particular time period. Reservation records about reservations for priority use of apparatuses are stored in a master machine. In the master machine, it is determined whether or not all the apparatuses on a reservation cooperation list are exclusively reserved during the same time period, by referring to the reservation records. When all the apparatuses which are reserved for priority use during the same time period, the master machine sends an exclusive release permission command to each subordinate machine reserved for priority use during the same time period among all the apparatuses.