According to an embodiment, a management apparatus connectable to a plurality of devices through a network includes storage, one or more processors, and an assignment transmitter. The storage stores therein management tree information in which node keys are respectively assigned to nodes and devices are respectively assigned to leaf nodes. The processors calculate similarity between attribute information representing an attribute of a new device and attribute information of devices already assigned in the management tree information. The processors determine a first leaf node to which the new device is to be assigned in the management tree information, based on the similarity. The assignment transmitter transmits, to the new device, at least one node key of node keys assigned to nodes on a path from a root node to the first leaf node in the management tree information.