1. An optical module comprising: a pair of first line sensors in which pixel arrays are arranged in a same direction; a pair of second line sensors in which pixel arrays are arranged in a direction which is different from the direction of said first line sensors; a pair of first optical systems which project an object image onto said first line sensors; and, a pair of second optical systems which project an object image onto said second line sensors, wherein one of lenses which are included in said first optical systems, is shared as one of lenses which are included in said second optical systems.