In a wiring substrate, a double data rate (DDR) memory and a memory controller controlling the DDR memory are mounted. Further, in the wiring substrate, plural equal-length wires connecting the DDR memory and the memory controller are formed. The plural equal-length wires include a differential transmission line, such as a clock wire transmitting a clock signal, which is connected via a common mode choke coil. The differential transmission line may have a wire length shorter than a wire length of another equal-length wire, by a wire length corresponding to delay time of a transmission signal due to the common mode choke coil.