1. A gateway apparatus comprising: a translator which is located on a boundary between a first network and a second network and performs protocol conversion of a control instruction, the first network being connected to at least one controller for executing the control instruction for at least one device, the second network being connected to at least one client which transmits the control instruction; and at least one aggregator which aggregates the plurality of control instructions, wherein the translator includes: an acquisition unit configured to acquire load information concerning a load on each of the controllers via the first network; a control instruction reception unit configured to receive a control instruction for a desired device from at least one client via the second network; a determination unit configured to determine whether the control instruction is an aggregation target, based on the load information on a controller corresponding to the device to which the control instruction is targeted, when the control instruction is received; a first transfer unit configured to transfer the control instruction to the aggregator corresponding to the control instruction, when it is determined that the control instruction is an aggregation target; and a second transfer unit configured to receive an aggregate control instruction from the aggregator, and wherein the aggregator includes: a third transfer unit configured to receive the control instruction from the translator; an aggregation unit configured to aggregate the plurality of control instructions which have been received into one aggregate control instruction; and a fourth transfer unit configured to transfer the aggregate control instruction to the translator.