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.