To provide an image forming apparatus having a sheet processing apparatus installed in an in-body space, capable of discharging sheets of different sizes without interfering with discharge operation of the sheet processing apparatus in a compact configuration. An image forming apparatus has a sheet binding unit disposed in an in-body space part thereof, a first conveying path for conveying the sheet discharged to the in-body space part toward the sheet binding unit, and a second conveying path for conveying the sheet discharged to the in-body space part toward a second stack tray that stacks thereon the sheet vertically below a first stack tray disposed outside the in-body space part. The second conveying path extends, inside the in-body space part, substantially horizontally between an image forming part and the sheet binding unit.