A conveyance control mechanism for a printer including an image forming unit forming an image on a sheet being conveyed on a conveyance route, includes a curl detector configured to detect a curl of the sheet conveyed on the conveyance route, in an upstream of the image forming unit on the conveyance route. The conveyance route controller may drive and stop the conveyance route differently depending on whether the curl detector detects a curl at either a front end or at a position other than the front end. When the curl detector detects a curl of the sheet, an image forming route where the image forming unit performs an image formation may be separated and retreated from the conveyance route and the sheet being conveyed may be discharged onto the retreated image forming route.