A medical knife (A), comprising: a pointed tip (4) a part (1) cutting includes a first oblique face (6) formed along an outer periphery, an edge formed of the first oblique face (6), and a second oblique face (8) formed inside the first oblique face (6) a part (2) of maximum width formed continuously from the part (1) cutting and a part (3) of body continuously formed from the part (2) of maximum width, in which a form of flat extension of the part (1) cutting, so that the width dimension is increased is created from one side of the sharp tip (4) to the part (2) of maximum width, wherein the first oblique face (6) is formed in an outer peripheral side of the second oblique face (8) in a portion from the portion (1) cutting through part (2) of maximum width to the body (3), in the flat shape at the part (2) of maximum width, the first oblique face (6) to form the edge intersects obliquely part (2) of maximum width of the medical knife (a) and the first oblique face (6) is formed along an outer periphery of the part (2) of maximum width to the side of the part (3) body, wherein the part (1) includes a lower cutting oblique face (7) formed at a lower side of the first oblique face (6), and edge is formed from the first oblique face (6) formed on an upper side and the lower oblique face (7) formed on the bottom side intersecting each other, and in which a surface is formed as substantially triangular wedge It has an intersection with the edge as a vertex and is defined by an end edge of the first oblique face (6) and an end edge of the bottom oblique face (7) whose area increases from the edge side to the side of the part (3) body on a side surface (11) of the medical knife (a) wherein the first oblique face (6) is formed so that the first oblique face (6) is located on the second oblique face (8) at least a part of the portion from the portion (2) of maximum width to the side of the part (3) of the body, and that the first oblique face (6) extends to one side of the pa
