To form a face which can be easily introduced into a counterpart member on the mounting part or the fitting part of a boot by providing a first mounting part to be engaged with an outer wheel on one of the end sides and a second mounting part to be engaged with a shaft part on the outer end side and forming the introduct on side end part of the inner peripheral face of the first or the second mounting part on an introduction face with the introduction side whose diameter becomes gradually larger.

The boot 1 formed of a rubber or an elastic plastic material has a first mounting part 2 to be fitted into a joint outer wheel formed on one of the end sides and a second mounting part 3 to be fitted into a shaft part formed on the outer end side. In addition, a bellows-type flexible part 4 is formed between the first mounting part 2 and the second mounting part 3. The flexible part 4 is entirely of a conical shape with the first mounting part 2 formed to be of a large diameter and the second mounting part 3 formed to be of a small diameter. The inner peripheral face of the first mounting part 2 has an easily introducible introduction face 7 of an arclike section formed so that the first mounting part 2 can be easily introduced into the outer wheel. Thus it is possible to easily form the introduction face 7 and assemble the mounting parts 2, 3 into the shaft joints without impairing the mounting parts 2, 3.