An apparatus for assigning time slots refers to a hierarchical structure when a predetermined number of time slots in one of a plurality of communication cycles is assigned to a communication apparatus, identifies an associated frame whose use status is to be changed to used by the assignment of the predetermined number of time slots for a group managed in a layer corresponding to the requested communication cycle, and makes determination to assign a frame belonging to a group in which a number of time slots, in the associated frame, whose use status is changed to used is smaller, to the communication apparatus.