On a circuit board configured to transmit a signal, a pulse transformer is provided on a path used for transmitting the signal of the circuit board. A shield member is provided on the circuit board to prevent noise, which is generated due to noise current flowing in a noise line pattern, from entering the pulse transformer. The shield member covers a part of a surface of at least one pulse transformer, the part intersecting concentric circles (which represent a magnetic field generated by the noise current) whose central axis extends along the direction in which the noise current flows.