The present invention is a Modbus-To-LwM2M converter for building a smart factory, the Modbus slave device communicating according to the Modbus protocol and the LwM2M server communicating according to the LwM2M protocol can communicate with each other so that the Modbus protocol and the LwM2M protocol are mutually converted. But; Converting a slave ID and a function code of the Modbus protocol-based message into an object type ID and an object instance ID of the LwM2M protocol-based message; The Modbus ID and data among the Modbus protocol-based messages are mapped to a resource ID and a value of the LwM2M protocol-based message, respectively. Accordingly, when applying the LwM2M protocol to be applied as the standard protocol of IoT, the initial cost required for smart factory construction is significantly reduced by converting Modbus protocol-based messages to LwM2M protocol-based messages to enable data communication with existing Modbus protocol-based equipment. I can make it.