A transmission device includes a temporary storage unit that is provided for each port receiving input data, stores the data temporarily, and outputs the temporarily stored data in response to a read enable signal, a storage unit that performs time-division multiplexing on the data output from the temporary storage unit in response to the read enable signal and stores the data, a flow monitoring unit that monitors a data flow for each of the ports, and a control unit that selects a temporary storage unit that is a read enable target from the temporary storage units corresponding to the ports to which the data is input, by a weighted round robin system in accordance with the data flow for each of the ports, and outputs the read enable signal to the selected temporary storage unit.