an image forming apparatus that detects a type of recording sheet and sets an image forming condition in accordance with the detected type of sheet includes a feeding unit that feeds a sheet , an image forming unit that forms an image on a sheet , and a reading unit that reads a picture of a surface of a sheet . a discriminating unit discriminates whether re - reading is necessary , on the basis of the picture . if so , another unit changes a reading condition of the reading unit and causes the reading unit to re - read the picture of the surface of the sheet . a detecting unit detects a type of sheet on the basis of the picture read by the reading unit , and a controlling unit controls an image forming condition on the basis of the result of the detection .