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.