1. A modular apparatus for a high-voltage direct-current transmission system, the apparatus comprising:a housing forming an external shape;
a display unit disposed on an inclined surface formed at a front lower portion of the housing and inclined with respect to the ground; and
a control board disposed in an installation space at a lower portion in the housing and controlling components in response to control signals transmitted from a controller located outside the housing through a cable,
wherein the display unit shows states of the components and is connected with the cable for connection with the controller, and
wherein a connector for connection with the cable is disposed at the control board.