To remove an undercut part from three-dimensional data of the inner face,
the program includes a surface model creating means to create a surface
model based on three-dimensional data of a gypsum model including an
abutment tooth, a cutting direction specifying means to specify a
direction of a cutting bar, and a surface model creating means to create
a surface model for machining by changing the three-dimensional data to
have new coordinates by determining a base axis in parallel with the
cutting bar in the surface model and plane moving coordinates of the
cutting bar, and converting the coordinates of a point which becomes an
undercut part, to be equal to the plane moving coordinates of a point
having a high height from a specified face rectangular to the base axis
at the opposite side of the occlusion face and a long distance from the
base axis.