Coordinate input apparatus

A coordinate input apparatus which detects a pointed position to an effective coordinate input region, comprising:

• a light projecting unit configured to project light parallelly to the effective coordinate input region;
• a reflection unit configured to retroreflect the light projected by said light projecting unit;
• a light receiving unit configured to receive light from one of said light projecting unit and said reflection unit;
• a first housing configured to incorporate at least two sensor units each including one of the light projecting unit and one of the light receiving unit;
• a second housing configured to incorporate at least two sensor units each including one of the light projecting unit and one of the light receiving unit;
• and
• a calculation unit configured to calculate the pointed position to the effective coordinate input region based on a variation of a light amount distribution obtained from said light receiving units of each of said first housing and said second housing,
• wherein in each of said first housing and said second housing,
• a field range of said light receiving unit is substantially parallel to the effective coordinate input region,
• an optical axis direction of said light receiving unit is a direction perpendicular to a line segment connecting barycenters of the at least two sensor units in a single housing, and
• the field range is set to be asymmetric to the optical axis direction.