The process for composing the polynomial spline function of order m which interpolates n data points is roughly divided into two stages: 1) The stage to construct the operator A which transforms B-spline coefficient vector c into sample-value vector s, 2) The stage to calculate the vector c. Then the effects on the number of computations for spline interpolation with respect to location of knots, boundary conditions, location of sampling points, and order of spline functions are evaluated.