A signal transmission apparatus used in a printed circuit board (PCB). The apparatus includes a differential pair composed of two transmission lines arranged side by side in the PCB. The differential pair includes a filter section arranged therein to filter noise of transmission signals of the differential pair. The filter includes a number of section pairs connected in series. Each section pair includes two sections arranged in the two transmission lines symmetrically. Every two adjacent sections are different in line width. A distance between the two transmission lines, and the line width of each of the sections are predetermined according to desired frequency bandwidth, and desired frequency response of the differential pair.