Abstract: A paper detecting apparatus capable of detecting the presence of the paper in the paper feed cassette and paper being fed along a duplex printing paper path by using a single sensor in an image forming machine having a duplex image forming function and feeding paper using a paper feed cassette. A paper detecting apparatus of an image forming machine according to the present invention includes an actuator pivotably disposed above a paper feed cassette in which paper is stacked and below a duplex printing paper path along which a first side copy moves and moved by the paper, and a paper sensor disposed next to the actuator that senses movement of the actuator and generates a signal, wherein the actuator pivots in a predetermined angle when no paper is stacked in the paper feed cassette or paper is being fed along the duplex printing paper path, and the paper sensor generates a signal upon sensing the pivoting actuator.