A differential current driving type data transmission system includes a line drive controller for outputting differential transmission signals and common mode line control signals, in response to a transmission signal; current sources for generating an excitation current and a base current and for driving positive/negative transmission lines with the base current; a first switch for selectively switching the excitation current to the positive/negative transmission lines, in response to the differential transmission signals; and a second switch for equalizing the positive/negative transmission lines within a common mode interval, in response to the common mode line control signals, wherein, in the common mode, the positive/negative transmission lines are driven at a level above or below an intermediate current level by a predetermined common mode current difference.