A steel sheet shape control method includes, (A) setting a target correction shape of the steel sheet at a position of an electromagnet to a curved shape, (B) measuring a steel sheet shape when electromagnetic correction is performed, (C) calculating the steel sheet shape in a nozzle position based on the steel sheet shape, (D) repeating (B) and (C) by resetting the target correction shape to a curved shape having a smaller amount of warp, (E) when the amount of warp of the steel sheet shape at the position of the nozzle is less than the upper limit value, (F) calculating vibration of the steel sheet at the position of the nozzle, and (G) adjusting a control gain of the electromagnet until amplitude of vibration is less than a second upper limit value when the amplitude of the vibration is equal to or more than the second upper limit value.

An image forming apparatus includes an apparatus main body, a post-processing device, a first magnetic body, and a second magnetic body. The apparatus main body includes an ejecting part configured to eject a sheet toward an ejecting space. The post-processing device is configured to be slidable between an attached position and a detached position. The post-processing device includes a post-processing part and a movable guide. The movable guide is movable between an ordinary position and an opening position. The first magnetic body magnetically attracts the second magnetic body so as to hold the movable guide at the opening position, in a state where the post-processing device is shifted to the detached position. The first magnetic body separates from the second magnetic body and releases magnetic attraction to the second magnetic body when the post-processing device slides from the detached position to the attached position.

Provided is a sheet feeding device and an image forming apparatus capable of performing sheet feeding by electrostatic adsorption at a low noise with a simple configuration. A first outer nip conveying roller 201b and a second outer nip conveying roller 202b that nip an adsorbing member 200 supported in a state an inside is loose by a first inner nip conveying roller 201a and a second inner nip conveying roller 202b are provided.

A steel sheet shape control method includes, (A) setting a target correction shape of the steel sheet at a position of an electromagnet to a curved shape, (B) measuring a steel sheet shape when electromagnetic correction is performed, (C) calculating the steel sheet shape in a nozzle position based on the steel sheet shape, (D) repeating (B) and (C) by resetting the target correction shape to a curved shape having a smaller amount of warp, (E) when the amount of warp of the steel sheet shape at the position of the nozzle is less than the upper limit value, (F) calculating vibration of the steel sheet at the position of the nozzle, and (G) adjusting a control gain of the electromagnet until amplitude of vibration is less than a second upper limit value when the amplitude of the vibration is equal to or more than the second upper limit value.

An image forming apparatus includes an apparatus main body, a post-processing device, a first magnetic body, and a second magnetic body. The apparatus main body includes an ejecting part configured to eject a sheet toward an ejecting space. The post-processing device is configured to be slidable between an attached position and a detached position. The post-processing device includes a post-processing part and a movable guide. The movable guide is movable between an ordinary position and an opening position. The first magnetic body magnetically attracts the second magnetic body so as to hold the movable guide at the opening position, in a state where the post-processing device is shifted to the detached position. The first magnetic body separates from the second magnetic body and releases magnetic attraction to the second magnetic body when the post-processing device slides from the detached position to the attached position.