A DC blocking device of a small size is disclosed. The disclosed DC blocking device may include: an internal conductor where RF signals are inputted; and an external conductor electrically connected to a ground; wherein the internal conductor has an insertion groove, and an insertion conductor is inserted into the insertion groove without touching the internal conductor and at a designated distance, and the diameter of the external conductor in the portion where the insertion conductor is inserted is set to be different from the diameter of another portion. The disclosed DC blocking device has the advantages of minimizing the spatial constraint when the DC blocking device is mounted on a mobile communication device, and of achieving suitable coupling even if the length of the part where coupling is achieved is reduced in the DC blocking device.