Method for manufacturing metal plate

A method for manufacturing a metal plate, wherein the metal plate includes a machining subject surface in at least one of a front surface and a rear surface of the metal plate in a thickness-wise direction, the machining subject surface is machined in a state in which the metal plate is held by a chuck in the thickness-wise direction, and the metal plate includes a first holding portion designed to be held by the chuck in the thickness-wise direction and a second holding portion located at a position separated from the first holding portion and designed to be held by the chuck in the thickness-wise direction, the method comprising:

• performing reference surface machining that machines a surface of the second holding portion that is to be held by the chuck into a predetermined shape in a state in which the first holding portion is held by the chuck;
• after performing the reference surface machining, releasing the first holding portion from the chuck and holding the second holding portion with the chuck;
• and
• machining the machining subject surface of the metal plate in a state in which the second holding portion is held by the chuck.