The outer peripheral surface of the boot attaching section of an outer joint member (2), when viewed in cross section, is non-cylindrical, with a large diameter section (22a) and a small diameter section (22b) appearing alternately. A thermoplastic elastomer boot (10) is composed of a large end side attaching section (12) adapted to fit on the boot attaching section of the outer joint member (2), a small end side attaching section (14) adapted to fit on a second rotational axis (3), and a bendable section (16) between the large and small end side attaching sections (12, 14), the large end side attaching section (12), when viewed in cross section, being shaped such that its outer peripheral surface is circular and its inner peripheral surface extends along the outer peripheral surface shape of the boot attaching section of the outer joint member (2), with thin-walled sections (12a) and thick-walled sections (12b) appearing alternately, the whole of the large end side attaching section (12) being filled with material.