In a three degrees of freedom parallel mechanism, a spindle head is carried by first and second movable support members to be movable along a Z-axis and to be pivotable along each of A and B-axes. The spindle head is jointed through three rods to drive sliders which are movable along three parallel linear guides secured stationarily. For jointing, there are employed spherical joints and universal joints. Kinematic parameters used in converting each command position of the movable body to target operational positions for three actuators of the Z, A and B-axes are compensated based on inversely converted command positions and inversely converted actually measured positions which have been gathered with the spindle head being located at positions of a suitable number, so that the kinematic parameters can be updated to those newest.