A noncontact measurement probe used when a workpiece is measured in a noncontacting manner upon exposure to light, the probe comprising: a light guiding path which guides a light, and surface plasmon conversion means which forms a light spot on the workpiece by way of surface plasmon and has a metal film which is provided on a light exit end of the light guiding path or in a vicinity of the light exit end of the light guiding path, the metal film having an aperture provided in line with an optical axis of the light guiding path, and a grating provided around the aperture on an exit-side surface of the metal film which faces the workpiece, wherein light from the light guiding path is converted into surface plasmon by means of the metal film, and the light spot is formed on a location, along an optical axis of the aperture, spaced from the surface plasmon conversion means by a desired distance determined from a width and a pitch of the grooves by means of interference among light beams acquired by means of re-conversion of the surface plasmon at respective grooves of the grating characterised in that the width and pitch of the grooves of the grating are set so as to become gradually smaller from the aperture toward a radial outside whereby the light spot is radiated on the location, along the optical axis of the aperture, spaced from the surface plasmon conversion means by a desired distance, wherein, provided that a distance from said exit-side surface of the metal film of the surface plasmon conversion means to the light spot along the optical axis of the aperture is taken as "f" and that a phase of light re-converted by the s th edge of the n th groove from the aperture toward a radial outside is taken as φ n,s, the grating is provided on the metal film such that the position x n, s of the s th edge of the n th groove from the aperture toward the radial outside fulfills the conditional equations and, wherein φ n, s + ω c f 2 + x n, s 2 − ω c f = 2 πm φ n, s = ∑ k = 0 n − 1 δ k + n eff ω c x n, s + Δ φ n, s where c: light speed of the light ω: an angular frequency of the light m: a number (an integer) of the groove from the aperture n eff: effective refractive index of the surface plasmon δ k: a phase lag of the surface plasmon achieved after the surface plasmon has transmitted through the k th groove from the aperture δ 0: an initial phase difference between spatially-propagated light from the aperture and the surface plasmon Δ φ n,s: a difference between the phase of surface plasmon reached at the s th edge of the n th groove from the aperture and the phase of light re-converted at the edge position of the groove. a light guiding path which guides a light, and surface plasmon conversion means which forms a light spot on the workpiece by way of surface plasmon and has a metal film which is provided on a light exit end of the light guiding path or in a vicinity of the light exit end of the light guiding path, the metal film having an aperture provided in line with an optical axis of the light guiding path, and a grating provided around the aperture on an exit-side surface of the metal film which faces the workpiece, c: light speed of the light ω: an angular frequency of the light m: a number (an integer) of the groove from the aperture n eff: effective refractive index of the surface plasmon δ k: a phase lag of the surface plasmon achieved after the surface plasmon has transmitted through the k th groove from the aperture δ 0: an initial phase difference between spatially-propagated light from the aperture and the surface plasmon Δ φ n,s: a difference between the phase of surface plasmon reached at the s th edge of the n th groove from the aperture and the phase of light re-converted at the edge position of the groove.