Patent ID: 7840163

Claim:
A position detecting device comprising: a plurality of detecting units that faces a mark-formation area of an object where marks are formed at predetermined intervals, and detects the marks at detection positions while the object is moving; a plurality of housing units each housing one of the detecting units; and a holding member that fixedly holds the housing units at fixed positions, wherein a total expansion amount of the housing units due to temperature change is substantially equal to an expansion amount of the holding member between the fixed positions due to temperature change, the total expansion amount representing a total amount of expansion of the housing units from a fixed-position plane to a detection-position plane in a direction parallel to a moving direction of the object, the fixed-position plane including one of the fixed positions and perpendicular to the moving direction of the object, and the detection-position plane including one of the detection positions and perpendicular to the moving direction of the object.