The present disclosure relates to an IoT communication system supporting connection between devices. The present disclosure provides an IoT device comprising a connect unit connecting with a sensor module, a processor performing data communication with the sensor module through the connect unit, a device memory storing data read from the sensor module through the data communication, and a communication module wirelessly transmitting the data stored in the device memory. The present disclosure connects an existing sensor module without a communication function with an IoT device equipped with a communication function and supports a standardized protocol between them, thereby enabling the IoT device to relay the sensor module's data and constructing a cost-effective IoT communication system.