The present disclosure provides a medical instrument, including a tubular main body； a plurality of operating lines； an operating part main body provided on the base end portion of the tubular main body； a bending operating part which is configured to bend a distal portion of the tubular main body； a path defining part which is configured to define a path of the operating line in the bending operating part； and a deviation preventive member which is configured to prevent the operating line from deviating from a path defined by the path defining part； wherein the operating line becomes in a relaxed state when the bending operating part is in a fixation position, while the operating line becomes in a strained state when the bending operating part is in an operation position.
