Abstract: A wafer exposure device includes a wafer stage. An optical exposure system exposes a wafer on the wafer stage. A sensor block measures a distance to a wafer provided on the wafer stage. The sensor block includes a plurality of height level sensors. Each height level sensor measures and outputs height level values. The wafer exposure device compares with one another the measured height level values outputted by respective height level sensors. The wafer exposure device calculates individual sensor position offset values to be attributed to the individual height level sensors. The wafer exposure device corrects the measured height level values output by the respective height level sensors using the calculated sensor position offset values of the respective height level sensor.