The data transmission device 1a of the present invention includes a driver 10 for sending data, a receiver 20 for receiving the data sent from the driver 10, a transmission line path 30 for connecting between the driver 10 and the receiver 20, and a variable impedance element 40 having a controllably variable impedance. The variable impedance element 40 is connected to the transmission line path 30. The data transmission line device 1a can reduce power consumption and occurrence of skew.