Provided is a manufacturing method for a rectangular can according to which it is possible to bring an angle formed by a step surface of a step provided in a rectangular can body and an inner wall surface of the rectangular can body closer to 90 degrees. In a step-forming step, using a die 310 that is provided on an outer wall surface side of a sidewall on which the step is to be formed, a mandrel 410 for sandwiching the sidewall between the mandrel 410 and the die 310 on the bottom side relative to a portion where the step is to be formed in the inner wall surface on which the step is to be formed, and a punch 420 for pressing the side opposite to the bottom side relative to the portion where the step is to be formed in the inner wall surface on which the step is to be formed and compressing the sidewall between the punch 420 and the die 310, the step is formed by performing multiple instances of a pressing operation performed by the punch 420.