To provide a partial thickening method of a tube body capable of rapidly executing partial heating at a low heating cost up to its inner surface side sufficiently and enlarging the quantity of protrusion toward the outside of a thickening part.

Freely and reparately movable heating means 20, 40 are provided in the longitudinal direction A of the tube body, an objective place B is heated with one heating means 20, heating means 20, 40 are apportioned and moved to both sides in the longitudinal direction A of the tube body with respect to a heating place C, and both sides of the heating place C are heated. Whereby, heating for the objective place B and heating for both sides of the heating place C are executed with a small gap S between the inner surface of the heating means and the outer surface 1a of the tube body. A compressing force in the longitudinal direction A of the tube body is imparted to the heating place C by a compressing force imparting means 13, whereby a part of material in the heating place C is successively thickened inward and outward in the part between the heating means 20, 40, and the thickened part which protrudes inward and outward in a ring shape with a desired quantity is formed in the part of a prescribed distance L from one end surface of the tube body 1.