A probe displacement command in a scanning measurement is generated according to a composite speed vector V: V=Gf·Vf+Ge·Ve+sp(p)·Gc·Vc2 wherein Vf is a vector along which a probe is displaced along a scanning path, Ve is a vector maintaining a deflection amount of the probe toward a work piece at a standard deflection amount. Vc2 is represented by (Vc1·q)q, Vc1 is a vector in a direction correcting a probe position such that a stylus tip is oriented along a scanning course, q is a vector given by a vector product of the normal line of a surface of the work piece and Vf, The normal direction of a measured surface is designated as Nw, p is a scalar product of Vc2 and Nw, and sg(p) is a function returning +1 or −1 in accordance with a value of p.