Disclosed is an apparatus of detecting a distributed reflection denial of service attack, including: a monitoring unit obtaining flow information including an IP and a port number of a source, an IP and a port number of a destination of data, and the number and the sizes of packets; a memory unit storing a flow table in which the flow information of the data, the packet number and the packet size are input; and a control unit detecting the DRDoS attack by using at least one of the number and the size of packets of the first entry and the flow information of the first entry.