1. A visible image forming apparatus comprising: a visible image forming unit that forms a visible image in the air; a controller that causes the visible image forming unit to form the visible image representing a print image; an operation detection unit that detects an operation of an operator performed on the print image displayed as the visible image by the visible image forming unit; and a print image processing unit that processes the print image according to the operation detected by the operation detection unit, wherein the controller causes the visible image forming unit to form, in the air, the visible image representing the print image processed by the print image processing unit, the operation detection unit detects a predetermined folding operation performed by the operator on the print image, the print image processing unit generates, upon receipt of a notice of the folding operation from the operation detection unit, a new print image representing a folded state of the print image formed as visible image in the air, and the controller causes the visible image forming unit to form, in the air, a visible image representing the print image newly generated by the print image processing unit.