An image forming apparatus is provided with an apparatus main body, an image forming assembly arranged in the apparatus main body, a sheet tray on which a sheet is to be placed, a conveyance unit detachably insertable into the apparatus main body, provided between the sheet tray and the image forming assembly and adapted to convey the sheet on the sheet tray toward the image forming assembly, an openable and closable cover member provided on a wall of the apparatus main body facing a downstream end of the conveyance unit in a sheet conveying direction, a vertical conveyance path defined at an inner side of the cover member by closing the cover member for further conveying the sheet conveyed by the conveyance unit upward, and a locking mechanism for preventing the conveyance unit from being pulled out from the apparatus main body with the cover member closed.