An image forming system includes: a sheet conveying section configured to convey a long sheet; an image forming/fixing section configured to execute an image forming/fixing operation to form and fix a toner image on the long sheet to be conveyed by the sheet conveying section; a skew detection section configured to detect a skew of the long sheet to be conveyed by the sheet conveying section; a skew correction section configured to execute a skew correction operation to correct the skew of the long sheet; and a control section configured to perform control to execute the skew correction operation when the skew has been detected in a first area where the skew correction operation does not affect the image forming/fixing operation, and perform control to execute the skew correction operation when the skew has been detected in a second area where the skew correction operation affects the image forming/fixing operation.