When the user touches a display screen, a touch-operated input device (7) detects a coordinate of a user-touched point on the display screen and a touch-input conversion program is executed to determine an axis, direction and speed of rotation of a three-dimensional object (40) on the basis of the user-defined coordinate, and give the information to a three-dimensional rendering program. The three-dimensional rendering program is executed to make a calculation for rotating the three-dimensional object (40) on the basis of the given information. The axis, direction and speed of the three-directional object rotation are repeatedly calculated in a fixed cycle only while the coordinate is kept defined by the user by continuously touching the display screen. Upon completion of each calculation, the results of calculation are given to the three-dimensional rendering program. Therefore, each time the user defines another point while continuously touching the display screen, the results of calculation of the axis, direction and speed of rotation change and thus the rotation of the three-dimensional object is dynamically changed. The present invention thus permits the user to intuitively make an manipulation, that is, rotation, movement, scale up or down, of a three-dimensional object with the use of the touch-operated input device.