To attach and remove long leg support members to and from a joint mechanism part through a simple operation.

This joint device includes a main block 6 provided at the crotch part of a patient to serve as the starting point of operation of the joint device, carriers 1 provided on both side parts of the main block 6 to make sliding movement relative to the main block 6 and to swing (oscillate) about the imaginary center point of rotation of the coxa of the patient (wearer), and attachments 2 attached to the upper ends of long leg support members 9 mounted at the leg parts of the patient and provided in such a way as to be capable of being attached to and removed from the carriers 1. Hook parts 21, 21' are provided at the side ends of each attachment 2. Engaging grooves 112, 112' which are engaged with the hook parts 21, 21' are provided at the side ends of the carriers 1. The hook part 21 is easily engaged in the engaging groove 112 by the swing of the carrier 1.