In this paper, an improving process of surface roughness in cylindrical plunge grinding with a super-soft grade resinoid bond wheel, whose bonding material is prepared by the interaction of polyvinyl alcohol and thermosetting plastics, is discussed, analyzing the ground surface profile, the topography of acting wheel surface and so on. Main conclusions obtained in this paper are as follows: (1) Minimizing phenomenon of surface roughness in which surface roughness decreases down to the minimum after start of grinding is remarkably occurred in plunge grinding process with a super-soft grade resinoid bond wheel. And the phenomenon is useful for improving surface roughness by grinding. (2) Decrease of number of simultaneously acting cutting edge by a rapid increase of wheel wear leads to worsen the surface finish just after the point of minimizing surface roughness. (3) The number of simultaneously acting cutting edge is obtained by ground surface profile, topography of acting wheel surface and interference wheel arc length.