In tree-based Wireless Sensor Networks (WSNs), multihop sensor nodes require a longer time to send sensed data to a sink node as the number of hops increases. The time taken for delivery of sensed data becomes a critical issue when a large WSN is realized. This paper proposes a new data collection scheme with rapid data delivery by utilizing so-called mobile agent technique in which no optimization of network structure for data collection is necessary. This scheme has little impact on data collection efficiency while not requiring a route optimization as it is required for a conventional data collection technique. The simulation results show that the proposed scheme achieves 63.1% reduction of time consumption taken for data collection compared with that taken by the conventional data collection technique in a network consisting of a sink node and 100 nodes.