There is provided a coating die for applying an insulation varnish around a wire conductor, comprising: a die body; and a die hole formed through the die body, the die hole including: an entry portion having an opening size monotonically decreasing along a conductor insertion direction; and a coating portion comprising a sub-portion having a constant opening size, in which: on an inner surface of the coating portion are provided at least four protrusions equally spaced in a circumferential direction of the inner surface, the protrusions projecting toward a center axis of the die hole; and each of the protrusions includes a portion with a height gradually increasing along the conductor insertion direction from a boundary between the entry portion and the coating portion. There can be formed an enameled wire having a thin and uniform insulation coating by using the invented coating die.