A robot in which two members constituting a joint shaft and supported in a relatively movable manner are each provided with a V-shaped groove having two sloped inner surfaces intersecting each other at a linear groove bottom extending orthogonally to a movement direction, or a V-shaped protrusion having two sloped outer surfaces intersecting each other at a linear ridge extending orthogonally to the movement direction. When the two members of the joint shaft are disposed in a predetermined operational position, the groove bottoms, the ridges, or the groove bottom and the ridge are disposed in alignment with each other.