A surgical instrument is disclosed. The apparatus is characterized in that a fixing means 17 is provided on a side of the main flame 15 for preventing the drive shaft 1 from rotating, the fixing means 17 includes a guided member 24 being capable of moving along a guide member 4 formed on the drive shaft 1 in the axial direction, and the guided member 24 is disposed between the nut 5 and the drive shaft 1. The pixel readout units having a brightness drop below the defined threshold are specified with regard to a cause of the brightness drop. The compliant alignment pin includes a tapered portion having a maximum diameter larger than a diameter of a boss hole in the base plate of the HGA.