A network system (103, 105, 107) comprising: one core node (111, 113, 115, 1) which is connected to an external network; and a plurality of slave nodes, wherein the core node (111, 113, 115, 1) is configured to transmit downlink packets to the plurality of slave nodes directly or through another slave node, each of the slave nodes includes: a plurality of directional antennas; and an antenna control unit that is configured to activate all or a part of the plurality of directional antennas, wherein in a reception waiting state, the antenna control unit of each of the slave nodes is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for receiving the downlink packets, and upon receiving downlink packets transmitted from the core node (111, 113, 115, 1), if received downlink packets contain a downlink forwarding packet to be transmitted to another slave node, with immediate generation of a transmission event, the antenna control unit is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for transmitting the downlink forwarding packet, and to forward the downlink forwarding packet characterized in that in a case where the core node (111, 113, 115, 1) transmits two downlink packets continuously and directly transmitted to the same slave node, the core node (111, 113, 115, 1) is configured to transmit the latter downlink packet after a certain fixed time period elapses, the fixed time period being equal to or more than a time period between a time when the former downlink packet is transmitted to the slave node and a time when the slave node that has directly received the former downlink packet ends communication processing with another slave node. one core node (111, 113, 115, 1) which is connected to an external network; and a plurality of slave nodes, wherein the core node (111, 113, 115, 1) is configured to transmit downlink packets to the plurality of slave nodes directly or through another slave node, each of the slave nodes includes: a plurality of directional antennas; and an antenna control unit that is configured to activate all or a part of the plurality of directional antennas, wherein in a reception waiting state, the antenna control unit of each of the slave nodes is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for receiving the downlink packets, and upon receiving downlink packets transmitted from the core node (111, 113, 115, 1), if received downlink packets contain a downlink forwarding packet to be transmitted to another slave node, with immediate generation of a transmission event, the antenna control unit is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for transmitting the downlink forwarding packet, and to forward the downlink forwarding packet characterized in that in a case where the core node (111, 113, 115, 1) transmits two downlink packets continuously and directly transmitted to the same slave node, the core node (111, 113, 115, 1) is configured to transmit the latter downlink packet after a certain fixed time period elapses, the fixed time period being equal to or more than a time period between a time when the former downlink packet is transmitted to the slave node and a time when the slave node that has directly received the former downlink packet ends communication processing with another slave node. a plurality of directional antennas; and an antenna control unit that is configured to activate all or a part of the plurality of directional antennas, wherein in a reception waiting state, the antenna control unit of each of the slave nodes is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for receiving the downlink packets, and upon receiving downlink packets transmitted from the core node (111, 113, 115, 1), if received downlink packets contain a downlink forwarding packet to be transmitted to another slave node, with immediate generation of a transmission event, the antenna control unit is configured to activate at least one directional antenna among the plurality of directional antennas, the at least one directional antenna serving for transmitting the downlink forwarding packet, and to forward the downlink forwarding packet characterized in that in a case where the core node (111, 113, 115, 1) transmits two downlink packets continuously and directly transmitted to the same slave node, the core node (111, 113, 115, 1) is configured to transmit the latter downlink packet after a certain fixed time period elapses, the fixed time period being equal to or more than a time period between a time when the former downlink packet is transmitted to the slave node and a time when the slave node that has directly received the former downlink packet ends communication processing with another slave node.