A data transmitter uses a transmission line including a ground conductor (305), a signal conductor (201), and an insulating material (3) which insulates them from each other. The insulating material includes a dielectric (320) exhibiting a nonlinear relationship between a generated electric field and dielectric polarization. The effective reactance per unit length of the transmission line changes depending on the signal voltage. Data is transmitted between integrated circuits (102) via the transmission line, achieving data transmission at a higher speed than a conventional one.