With the increase in the number of Internet of Things (IoT) devices, many applications using the data accumulated from IoT devices have been proposed. Consequently, privacy violation due to data disclosure is becoming a problem. Data anonymization is a technique for publishing data while preserving data privacy and is an effective method for solving the problem of privacy violation. There are several requirements for implementing anonymization systems suitable for IoT devices, where the amount of hardware and software resources, function extensibility, and processing throughput are limited. To satisfy these requirements, anonymization hardware for anonymizing data packets from IoT devices is proposed. The proposed hardware is allocated on the intermediate location of network and anonymizes the data packet stream from IoT devices transparently. The proposed anonymization process does not affect data communication or routing. This transparency allows an additional anonymization function to be installed on all types of IoT devices without modifying the devices. The proposed hardware allows IoT devices to anonymize the data packet stream. To reduce the latency and achieve transparent anonymization at a low cost, the proposed anonymization hardware was implemented using a field-programmable gate array. The throughput and latency of the testbed of the proposed hardware were 1,286 Mbps and 330 ns, respectively. The power consumption of the proposed hardware was lower than that for a software implementation.