A safety device for a machine, such as a press brake, has a light transmitter, a light receiver and an evaluation unit. The light receiver is coupled to a moving machine part such that it runs ahead of a front edge of the machine part during the operational movement. The light transmitter comprises a light source having a predominantly incoherent radiation for generating a light beam that runs substantially parallel to the edge and illuminates the light receiver. The light receiver has an image sensor with a plurality of pixels for recording a spatially resolved image of the light beam, and it has an imaging optics having a focal point and an aperture stop which is substantially arranged at the focal point.