Abstract: Control apparatus controls the operation of a trailing edge folder in a carton blank folding machine. The folding machine has conveyor means for continuously advancing blanks in a predetermined direction in untimed relationship to one another along a generally horizontal path. The trailing edge folder has a rotatable shaft mounted below and transverse to the path. The shaft has mounted thereon for rotation therewith one or more arms which extend outwardly from the axis of the shaft. Folding heads extend from the distal ends of the arms. The control apparatus has a sensor which produces a trailing edge signal indicating the departure of the trailing edge of a blank from a first location along the path upstream of the folder. At the end of a determined interval after the trailing edge signal the shaft is rotated in the direction in which the carton is travelling so that a head on the shaft comes into contact with the trailing panel of the blank, and folds it over about 180.degree..