An image forming apparatus includes a fixing unit, detection units, and a control unit. The control unit switches a sheet speed at the fixing unit to either a first or second sheet speed that is faster than the first sheet speed based on a first detection unit signal where the control unit detects that both a loop amount of a sheet loop at second and third detection unit positions are greater than or less than a predetermined amount. The control unit sets the fixing unit sheet speed as a predetermined sheet speed between the first and second sheet speed where the control unit detects that one of two loop amounts detected the second and third detection units is greater than the predetermined amount when the other one of the two loop amounts is less than the predetermined amount.