A method for forming a coating film on an internal surface of an elongated tube, includes longitudinally holding the elongated tube, applying a coating solution to the internal surface of the elongated tube; and drying the coating solution while carrying out a heat process for sequentially heating the elongated tube by using a heat source. The heat process includes adjusting the descending rate of the heat source so that a through-hole in the elongated tube is clogged with the coating solution whose viscosity is reduced by heating of the heat source, and sucking the through-hole in the elongated tube from the lower side thereof so that a portion of the through-hole that is clogged with the coating solution moves downwards along the elongated tube.