A gateway apparatus that connects a multi-hop network of tree structure formed of node apparatuses to other network, comprising a grouping unit that groups, for each representative node apparatus having a direct link to the gateway apparatus in the tree structure, the nodes belonging to a subtree having same representative node as a root, into a node group, an interference group specifying unit that specifies a node group in which packet communication in the node group is subjected to an interference of a degree exceeding a threshold as an interference group, and a slot allocation unit that allocates some one time slot among a plurality of time slots included in a frame to one interference group among a plurality of interference groups, and allocates another time slot among the plurality of time slots to another interference group among the plurality of interference groups.