A manufacturing method of a secondary battery having an electrode assembly placed in a prismatic container, wherein an upper part of an inside of an electrolyte injection hole formed in a base plate mounted to an open upper end of the prismatic container is configured to have a chamfered structure in which a diameter of the electrolyte injection hole is gradually decreased downward, a lower part of the inside of the electrolyte injection hole is configured to have a non-chamfered structure, the chamfered structure is formed in an irregular shape to increase a length of an electrolyte leakage route along which an electrolyte leaks out of the secondary battery, and comprising a sealing member pressed into the electrolyte injection hole, wherein the sealing member is deformed so as to correspond to an internal structure of the electrolyte injection hole such that the electrolyte injection hole is sealed by the sealing member, the manufacturing method comprising: (a) placing an electrode assembly in a prismatic container; (b) mounting a base plate having an electrolyte injection hole, an upper part of an inside of which is configured to have a chamfered structure in which a diameter of the electrolyte injection hole is gradually decreased downward and which is formed in an irregular shape, and a lower part of the inside of which is configured to have a non-chamfered structure, to an open upper end of the prismatic container; (c) injecting an electrolyte into the prismatic container through the electrolyte injection hole; and (d) pressing a sealing member in a state in which the sealing member is located on the electrolyte injection hole to deform the sealing member so as to correspond to an internal structure of the electrolyte injection hole such that the electrolyte injection hole is sealed by the sealing member, wherein the step (d) comprises: locating the sealing member on the electrolyte injection hole in a state in which the prismatic container is fixed by a die; moving a press downward while rotating the press to press the sealing member into the electrolyte injection hole; and plastically deforming the sealing member such that the electrolyte injection hole is sealed by the sealing member, wherein the step further comprises repeatedly reciprocating the press in a vertical direction in a state in which the press is moved upward by a predetermined height after the press had pressed the sealing member through one downward movement, to press the sealing member. (a) placing an electrode assembly in a prismatic container; (b) mounting a base plate having an electrolyte injection hole, an upper part of an inside of which is configured to have a chamfered structure in which a diameter of the electrolyte injection hole is gradually decreased downward and which is formed in an irregular shape, and a lower part of the inside of which is configured to have a non-chamfered structure, to an open upper end of the prismatic container; (c) injecting an electrolyte into the prismatic container through the electrolyte injection hole; and (d) pressing a sealing member in a state in which the sealing member is located on the electrolyte injection hole to deform the sealing member so as to correspond to an internal structure of the electrolyte injection hole such that the electrolyte injection hole is sealed by the sealing member, wherein the step (d) comprises: locating the sealing member on the electrolyte injection hole in a state in which the prismatic container is fixed by a die; moving a press downward while rotating the press to press the sealing member into the electrolyte injection hole; and plastically deforming the sealing member such that the electrolyte injection hole is sealed by the sealing member, wherein the step further comprises repeatedly reciprocating the press in a vertical direction in a state in which the press is moved upward by a predetermined height after the press had pressed the sealing member through one downward movement, to press the sealing member. locating the sealing member on the electrolyte injection hole in a state in which the prismatic container is fixed by a die; moving a press downward while rotating the press to press the sealing member into the electrolyte injection hole; and plastically deforming the sealing member such that the electrolyte injection hole is sealed by the sealing member,