A device for detecting edges of sheet-shaped print materials (1), especially of transparencies, that are moved along a transport path through a sheet-processing machine has a beam transmitter (31) and a beam receiver (32), whereby beam transmitter (31) and beam receiver (32) are mounted on different sides of the transport path in such a way that the beam path forms an acute angle to the surface of the sheet-shaped print material (1). Electronics (36) evaluate the beam received at the beam receiver (32), whereby the beam receiver (32) is at a lesser distance to the transport path in comparison to the beam transmitter (31).