PURPOSE: To improve cutting quality and to prevent giving pains to a patient by forming the grain of the direction intersecting approximately orthogonally with the central axis of the square suturing needle and the grain of the direction along the central axis on the surface constituting the cutting edge of the square suturing needle.

CONSTITUTION: The horizontal grain 8 of the direction intersecting approximately orthogonally with the central axis of the square needle and the vertical grain 9 of the direction along the central axis are formed on the surface 2 constituting the cutting edge 3. The horizontal grain 8 and the vertical grain 9 are formed as microgrooves several μm to several tens μm depth. Many pieces of microruggedness 10a, 10b are formed on the surface 2 by the horizontal grain 8 and the vertical grain 9. Slight spacings are, therefore, formed between the biotissue and recessed parts 10a even if the botissue cut by the cutting edge 3 come into pressurized contact with the surface 2 when such square needle is passed into the biotissue. The biotissue is thus prevented from coming into tight contact with the surface 2 over the entire surface thereof. The friction resistance between the biotissue and the square needle is decreased in this way and the operator's feel of cutting is improved.