A firmware updating method for the new node includes (a) a new node searching for neighbor nodes located within a predetermined distance, (b) the new node designating a parent node among the searched neighbor nodes, (c) in the case where the plurality of nodes include a join receiving state for joining the new node to the wireless sensor network, the designated parent node and the new node establishing a communication link by using the join receiving state, (d) the parent node transmitting firmware to the new node through the established communication link and (e) the new node receiving the firmware from the parent node, updating existing firmware with the received firmware, and driving the updated firmware to be jointed to the wireless network.