In a system for producing an animation on a computer by use of keyframes, shapes are drawn on the basis of the positions of vertices designated by a user without direct manipulation of control points for Bézier curve so that there is little problem even in the case where a line drawing of each handwritten keyframe is broken discontinuously. To this end, Bézier curves are automatically generated to draw shapes by fetching a plurality of keyframes written on paper into a computer and then setting vertices of only first one of the keyframes. On this occasion, an optimum path connecting the position of each of the set vertices to the current cursor position is calculated. The path is approximated by a cubic equation. A Bézier curve is defined on the basis of comparison of coefficients of respective terms in the equation with coefficients in the Bézier curve. For each of keyframes after the first keyframe, control points for Bézier curve are re-calculated to reshape shapes by moving vertices of the previously drawn shapes and by dragging the neighborhood of the contour of the keyframe.