A processing device which can execute a plurality of threads includes: an execution unit which executes a command; a supply unit which supplies a command to the execution unit; a buffer unit which holds the command supplied from the supply unit; and a control unit which manages the buffer unit. The buffer unit has a set of buffer elements. Each of the buffer elements has a data unit for storing a command and a pointer unit for defining a connection relationship between the buffer elements. The control unit has a thread allocation unit which allocates a sequence of buffer elements whose connection relationship has been defined by the pointer unit for respective threads executed by the processing device.