A capacitor comprises: a capacitor module including a capacitor device, a first busbar electrically connected with a thermally-sprayed surface of the capacitor device and having a first lead terminal on an exposed side, a second busbar electrically connected with the other thermally-sprayed surface of the capacitor device and having a second lead terminal on an exposed side, and an insulating sheet disposed between the first busbar and the second busbar to insulate an overlap region; a plastic case having a 3D space formed by four sides and a bottom to accommodate the capacitor module and having an open top; a metallic external wall is formed outside one side of the four sides or the bottom of the plastic case; and a filler permeating in a gel or fluid state into the space between the capacitor module and inner walls of the plastic case.