Abstract: An apparatus for checking linear dimensions of a workpiece (10) according to the shadow casting technique, including a bed (1), a first support structure (5, 6) sustained by the bed for supporting the workpiece, a second support structure (4), optical sources (22-25) coupled to the second support structure (4) for generating associated beams of light, a plurality of linear photosensitive devices (26-29) coupled to the second support structure (4) for receiving the beams of light after they have been intercepted by the workpiece, and detecting circuits (20, 21) connected to the photosensitive devices (26-29). The optical sources (22-25) are arranged in two units (22, 23; 24, 25) at opposite sides with respect to the workpiece, and the photosensitive devices (26-29) are also arranged in two units (26, 27; 28, 29) located at opposite sides with respect to the workpiece.