An image forming apparatus comprising: an image forming means configured to form an image based on an image forming condition on a sheet; a fixing means configured to fix the image on the sheet; a reading means configured to read a detection image on a sheet which passes a reading area downstream of the fixing means in a conveyance direction along which the sheet having the detection image formed thereon is conveyed; a reference member (352, 355); and a control means configured to: control the image forming means to form the detection image on a sheet; control the fixing means to fix the detection image on the sheet; control the reading means to read the detection image on the sheet; adjust the image forming condition based on a reading result of the detection image by the reading means; and control the reading means to read the reference member (352, 355) to execute shading correction of the reading means based on a reading result thereof, characterized in that the control means is configured to control the image forming means to form the image and the detection image on a same sheet, the control means is configured to control the reading means (352, 355) to read the detection image on the same sheet having the image formed thereon, in a case where the shading correction is executed while a plurality of sheets on which the image and the detection image are formed are passing the reading area, the control means is configured to, without reading the detection image on the sheet passing through the reading area by the reading means, control the reading means to read the reference member (352, 355) while continuing passing of the plurality of sheets through the reading area. an image forming means configured to form an image based on an image forming condition on a sheet; a fixing means configured to fix the image on the sheet; a reading means configured to read a detection image on a sheet which passes a reading area downstream of the fixing means in a conveyance direction along which the sheet having the detection image formed thereon is conveyed; a reference member (352, 355); and a control means configured to: control the image forming means to form the detection image on a sheet; control the fixing means to fix the detection image on the sheet; control the reading means to read the detection image on the sheet; adjust the image forming condition based on a reading result of the detection image by the reading means; and control the reading means to read the reference member (352, 355) to execute shading correction of the reading means based on a reading result thereof, control the image forming means to form the detection image on a sheet; control the fixing means to fix the detection image on the sheet; control the reading means to read the detection image on the sheet; adjust the image forming condition based on a reading result of the detection image by the reading means; and control the reading means to read the reference member (352, 355) to execute shading correction of the reading means based on a reading result thereof, characterized in that the control means is configured to control the image forming means to form the image and the detection image on a same sheet, the control means is configured to control the reading means (352, 355) to read the detection image on the same sheet having the image formed thereon, in a case where the shading correction is executed while a plurality of sheets on which the image and the detection image are formed are passing the reading area, the control means is configured to, without reading the detection image on the sheet passing through the reading area by the reading means, control the reading means to read the reference member (352, 355) while continuing passing of the plurality of sheets through the reading area.