If a random number is larger than a selection coefficient SF, a room unit RU is given a high priority for disposition in a map area. If the random number is not larger than the selection coefficient, no room unit is disposed on the map area. Also, if a selected open door is a door set in a room unit, the selection coefficient is multiplied by a multiplication factor, and then the multiplication result and the random number are compared. As the multiplication factor is larger, a passage unit is given a higher priority for disposition on the map area. By adjusting the selection coefficient and the multiplication factor, it is possible to generate a map in consideration of a ratio of units of two types to be disposed on the map area and an affinity between these units for connection.