A ray processing method, comprising: selecting , from among a plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) based on a state of each of the plurality of traversal units, a traversal unit to process traversal of an input ray; and processing , by way of a processor, the traversal of the input ray using the selected traversal unit, wherein the state of each of the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) is determined based on a state of each of one or more rays that are processed by each of the plurality of traversal units; wherein the traversal unit is selected from among the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) based on an age of each of the plurality of traversal units; and wherein the age of each of the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) is determined based on an age of each of the one or more rays that are processed by each of the plurality of traversal units, and the age of each of the one or more rays is information indicating a duration of time in which the respective ray has been input into the respective traversal unit (100, 340-1, 340-2, 340-3, 340-4, 340-5) and remains in the respective traversal unit (100, 340-1, 340-2, 340-3, 340-4, 340-5), and is determined based on a number of times that traversal of each of the one or more rays is repeatedly processed by the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5); characterized in that the selected traversal unit is a traversal unit having a greatest age among traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) having the smallest number of rays within an input buffer among the plurality of traversal units or a traversal unit having the greatest age among traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) for which an input buffer is available. selecting , from among a plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) based on a state of each of the plurality of traversal units, a traversal unit to process traversal of an input ray; and processing , by way of a processor, the traversal of the input ray using the selected traversal unit, wherein the state of each of the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) is determined based on a state of each of one or more rays that are processed by each of the plurality of traversal units; wherein the traversal unit is selected from among the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) based on an age of each of the plurality of traversal units; and wherein the age of each of the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) is determined based on an age of each of the one or more rays that are processed by each of the plurality of traversal units, and the age of each of the one or more rays is information indicating a duration of time in which the respective ray has been input into the respective traversal unit (100, 340-1, 340-2, 340-3, 340-4, 340-5) and remains in the respective traversal unit (100, 340-1, 340-2, 340-3, 340-4, 340-5), and is determined based on a number of times that traversal of each of the one or more rays is repeatedly processed by the plurality of traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5); characterized in that the selected traversal unit is a traversal unit having a greatest age among traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) having the smallest number of rays within an input buffer among the plurality of traversal units or a traversal unit having the greatest age among traversal units (100, 340-1, 340-2, 340-3, 340-4, 340-5) for which an input buffer is available. <EOS>