An apparatus for detecting the position, in a predetermined direction normal to a substrate, of at least one measurement point in a detection area on the substrate, includes:a projection device for projecting a light-dark pattern consisting of a repetitive pattern of light and dark portions in a predetermined detection direction onto substantially the entire detection area;a photoelectric detection device for detecting reflection light from the substrate, and outputting a photoelectric signal having a waveform representing the contrast of an image of the light-dark pattern in the detection direction;a device for detecting the position of a waveform representing a dark portion of the light-dark pattern corresponding to the measurement point in the waveform of the photoelectric signal; anda measurement device for measuring the position, in the predetermined direction, of the measurement point based on a deviation between the detected waveform position and a predetermined reference position.