A surgical instrument for performing treatment to a treatment target portion includes a cylindrical elongated member； a treatment part, and a connection part. The connection part includes a first turning axis part provided to the elongated member, a second turning axis part provided to the treatment part, a first rolling guide part that is provided to the elongated member and includes a circular-arc-shaped part coaxial with the first turning axis part, a second rolling guide part that is provided to the treatment part and includes a rolling guide part including a circular-arc-shaped part coaxial with the second turning axis part, the rolling guide part rollingly contacting the first rolling guide part, and an engaging part that brings the treatment part and the elongated member into an engaging state. The connection part is detachable between the first turning axis part and the second turning axis part.
