Original reading unit, image forming apparatus and image scanner

An original reading unit comprising:

• a unit base;
• a transparent original support plate attached to the unit base;
• and
• multiple sensor assemblies arranged in a zigzag pattern to form on the unit base a first array of the sensor assemblies extending in a main scanning direction for performing a first reading of an original document and a second array of the sensor assemblies extending in the main scanning direction for performing a second reading of the original document following the first reading by the first array of the sensor assemblies;
• wherein each of the sensor assemblies includes:
• a sensor holder mounted for undergoing pivotal movement about a single rotation center as a fulcrum along a wall of the unit base to bring the sensor holder to a predetermined position so that the sensor holder can be fixed to the wall of the unit base;
• a line sensor mounted relative to the sensor holder so as not to be shifted in the main scanning direction or in a sub-scanning direction, and mounted for undergoing movement in an approaching or a separating direction so as to be brought into contact with or separated from, respectively, the wall of the unit base and the original support plate;
• and
• a focus setup unit that moves the line sensor in the approaching or separating direction and that positions the line sensor at a location whereat focus can be adjusted.