Abstract: A tire changer is provided for mounting/dismounting a tire to/from a wheel rim. The tire changer includes a tire fixing device mounted to a support arm and including a transmission cylinder that is rotatably mounted to the support arm and driven by a power device, a first retention member, a second retention member, and a fastening member. The transmission cylinder receives therein a transmission shaft having an end projecting outside the cylinder and forming a fastening section. The first and second retention members are mounted to the transmission shaft and both form a slope that is set in abutting engagement with an inside surface of a fixing bore formed in the rim. The fastening member is coupled to the fastening section to be positioned against the second retention member to thereby secure the rim between the first and second retention members.