A surgical power transmission adapter is interposed between a surgical instrument and a power unit configured to drive the surgical instrument. The adapter connects the surgical instrument to the power unit. The adapter includes a power transmission unit. The power transmission unit includes a first region which is in contact with a clean region that is subjected to sterilization processing and a second region which is in contact with an unclean region that is not subjected to the sterilization processing. The unit makes translatory movement to transmit power generated in the power unit to the surgical instrument. A range of the translatory movement of the power transmission unit is set in such a manner that the first region is placed in the clean region and the second region is placed in the unclean region even if the power transmission unit makes the translatory movement.
