To provide satisfactory rigidity to torsion without loosing the flexibility in the area of the middle foot part of a ski boot by providing a set of reinforcing members extending along the respective lateral side walls of a shell between the middle part of a sole and the rear area of the shell.

This ski boot 1 comprises a plastic shell 2, a sole 3, and a leg member 4 hinged by a hinge 13 in the heel part to the shell 2. The shell 2 has a set of lateral walls 7 forming a front opening closed by a tongue member 8 and a flexible part 11 extending from one side of the sole 3 to the other side across the shell 2. The ski boot 1 also has a control device 14 for regulating the inclination of the leg member 4 to the shell 2. Further, the shell 2 has a set of reinforcing members 17 and 18 formed by both standing outside ribs on the surfaces of the lateral walls 7, and these members 17 and 18 formed a base 24 for fixing the device 14, which is locked by a pin 25.