An ultracapacitor comprising: a case (110; 210) having a cylindrical shape of which one end is closed and the other end is opened; a bare cell (120; 220) placed inside the case and shaped like a winding element comprising a positive electrode, a negative electrode and a separator; a first internal terminal arranged in a closed region of the case (110; 210) within the case (110; 210) and connected to a positive electrode of the bare cell (120; 220); a second internal terminal arranged in an open region of the case (110; 210) within the case (110; 210) and connected to a negative electrode of the bare cell (120; 220); and an external terminal (150; 250) connected to the second internal terminal at an outside of the case (110; 210), characterized in that each of the first and second internal terminals (130, 140) comprises a case coupling plate (136, 146; 236, 246) having a flat bottom surface (136a, 146a; 236a, 246a) formed with a plurality of electrolyte injection holes (136b, 146b; 236b, 246b) on a surface thereof, and a lateral surface (136c, 146c; 236c, 246c) arranged perpendicularly along an outer circumference of the bottom surface (136a, 146a; 236a, 246a), the bottom surface (136a, 146a; 236a, 246a)) of the case coupling plates (136, 146; 236, 246) is in contact with and laser-welded to the bare cell (120; 220), and the lateral surface (136c, 146c; 236c, 246c) of the case coupling plates (136, 146; 236, 246) is formed in a flat surface, and the lateral surfaces of the case coupling plate (136; 236) of the first internal terminal and of the case coupling plate (146; 246) of the second internal terminal are curved in a radially inward direction and coupled to the case (110; 210) by clamping process. a case (110; 210) having a cylindrical shape of which one end is closed and the other end is opened; a bare cell (120; 220) placed inside the case and shaped like a winding element comprising a positive electrode, a negative electrode and a separator; a first internal terminal arranged in a closed region of the case (110; 210) within the case (110; 210) and connected to a positive electrode of the bare cell (120; 220); a second internal terminal arranged in an open region of the case (110; 210) within the case (110; 210) and connected to a negative electrode of the bare cell (120; 220); and an external terminal (150; 250) connected to the second internal terminal at an outside of the case (110; 210), characterized in that each of the first and second internal terminals (130, 140) comprises a case coupling plate (136, 146; 236, 246) having a flat bottom surface (136a, 146a; 236a, 246a) formed with a plurality of electrolyte injection holes (136b, 146b; 236b, 246b) on a surface thereof, and a lateral surface (136c, 146c; 236c, 246c) arranged perpendicularly along an outer circumference of the bottom surface (136a, 146a; 236a, 246a), the bottom surface (136a, 146a; 236a, 246a)) of the case coupling plates (136, 146; 236, 246) is in contact with and laser-welded to the bare cell (120; 220), and the lateral surface (136c, 146c; 236c, 246c) of the case coupling plates (136, 146; 236, 246) is formed in a flat surface, and the lateral surfaces of the case coupling plate (136; 236) of the first internal terminal and of the case coupling plate (146; 246) of the second internal terminal are curved in a radially inward direction and coupled to the case (110; 210) by clamping process.