Image forming apparatus and image forming method

An image forming method comprising:

• controlling, on the basis of a condition for use of a recording medium, an opening and closing operation of a nipping device provided on a retaining roller, which retains the recording medium on a surface of the retaining roller, and configured to mechanically nip the recording medium between the nipping device and the surface of the retaining roller according to the opening and closing operation;
• attracting and retaining the recording medium on the surface of the retaining roller with a device different from the nipping device;
• and
• forming an image on the recording medium retained on the surface of the retaining roller.

A sheet processing apparatus comprising:

• a retaining roller configured to retain a recording medium on a surface of the retaining roller and rotate;
• a nipping device capable of operating to open and close and configured to hold the recording medium between the nipping device and the surface of the retaining roller in a closed state to mechanically retain the recording medium;
• a retaining device different from the nipping device and configured to retain the recording medium on the surface of the retaining roller;
• and
• a controller configured to control, on the basis of a condition for use of the recording medium, the nipping device to nip the recording medium between the nipping device and the surface of the retaining roller.