The present invention relates to an electrode unit (10, 20) for an electric vacuum capacitor comprising a band-shaped capacitor plate (11, 21) with a height H, wherein the band-shaped capacitor plate (11, 21) is wound in a spiral with a maximum diameter Dmax and a constant distance between successive turns, wherein the band-shaped capacitor plate (11, 21) comprises a first longitudinal edge (11a, 21a) attached to a supporting part (12) and a second longitudinal edge (11b, 21b), the second longitudinal edge (11b, 21b) being free, wherein at the outer extremity of the spiral, the first longitudinal edge (11a, 21a) and the second longitudinal edge (11b, 21b) are connected by an inclined edge (11c, 21c) such that the first longitudinal edge (11a, 21a) is longer than the second longitudinal edge (11b, 21b), wherein the inclined edge (11c, 21c) forms with the longitudinal axis (B) of the band-shaped capacitor plate (11, 21) an angle α less than or equal to an angle αmax=(45°·π/180°). The invention relates also to a vacuum capacitor (30) comprising at least one electrode unit (10, 20) according to the present invention.