A power conversion device used in a DC power transmission system having a multipolar configuration includes: a self-excited AC/DC converter configured to convert electric power between an AC system and a main line; and a controller. The controller is configured to: receive an input of a current value between a neutral point and a DC terminal of the AC/DC converter; control an operation of the AC/DC converter; and control a switch to be opened and closed, the switch being provided between the DC terminal and the neutral point. When the current value is equal to or greater than a predetermined threshold value, the controller stops a plurality of cells and subsequently closes a bypass switch. When the current value is equal to or greater than a predetermined threshold value, the controller opens the switch.