A medical knife of the invention having a cutting edge formed along the outer periphery of a blade portion includes a shank; and a blade portion formed continuously from the shank, the blade portion includes a tip portion including a tip whose projected plane shape is formed at an extreme end portion; a maximum width portion having a largest width: a side surface portion formed between the tip portion and the maximum width portion; a cutting edge; a first slanting surface formed along the cutting edge; and a second slanting surface formed along the first slanting surface, wherein the first slanting surface constituting the tip portion has a width larger than that of the first slanting surface constituting the side surface.