A method for manufacturing a safety vent of a cap plate for a secondary battery, the method comprising: a safety vent forming step in which a material plate of a cap plate is put on a top surface of a lower forming portion of a press, which includes a lower forming portion formed with a long elongated hole extending back and forth and provided therein with a lower elevating mold that defines a peripheral discharge part,, and an upper forming portion provided therein with an upper elevating mold, a material is discharged to the peripheral discharge part to form a discharge material portion while forming a safety vent having a groove shape and formed at a lower portion thereof with a vent plate through downward movement of the upper forming portion and the upper elevating mold and upward movement of the lower elevating mold, and the safety vent is formed through upward movement of the upper forming portion and the upper elevating mold and downward movement of the lower elevating mold; a discharge material portion cutting and removing step in which the discharge material portion of the material plate is inserted into a discharge material portion insertion hole by putting the safety vent material plate formed with the safety vent onto the top surface of the lower forming portion of the press having the lower forming portion formed with the discharge material portion insertion hole accommodating a cutting device for cutting an upper portion of the discharge material portion, and the upper portion of the discharge material portion is cut by operating the cutting device for the discharge material portion so as to remove the discharge material portion; and a lower surface flattening forming step in which the material plate from which the upper portion of the discharge material portion is cut is put on the top surface of the lower forming portion of the press having the lower forming portion with a flat top surface and the upper forming portion formed at a lower portion thereof with a safety vent insertion part, a bottom surface of the material plate is flattened through downward movement of the upper forming portion, and the upper forming portion is moved up. a safety vent forming step in which a material plate of a cap plate is put on a top surface of a lower forming portion of a press, which includes a lower forming portion formed with a long elongated hole extending back and forth and provided therein with a lower elevating mold that defines a peripheral discharge part,, and an upper forming portion provided therein with an upper elevating mold, a material is discharged to the peripheral discharge part to form a discharge material portion while forming a safety vent having a groove shape and formed at a lower portion thereof with a vent plate through downward movement of the upper forming portion and the upper elevating mold and upward movement of the lower elevating mold, and the safety vent is formed through upward movement of the upper forming portion and the upper elevating mold and downward movement of the lower elevating mold; a discharge material portion cutting and removing step in which the discharge material portion of the material plate is inserted into a discharge material portion insertion hole by putting the safety vent material plate formed with the safety vent onto the top surface of the lower forming portion of the press having the lower forming portion formed with the discharge material portion insertion hole accommodating a cutting device for cutting an upper portion of the discharge material portion, and the upper portion of the discharge material portion is cut by operating the cutting device for the discharge material portion so as to remove the discharge material portion; and a lower surface flattening forming step in which the material plate from which the upper portion of the discharge material portion is cut is put on the top surface of the lower forming portion of the press having the lower forming portion with a flat top surface and the upper forming portion formed at a lower portion thereof with a safety vent insertion part, a bottom surface of the material plate is flattened through downward movement of the upper forming portion, and the upper forming portion is moved up.