PURPOSE: To decide the optimum assembling sequence to assemble a product from components and units in a short time.

CONSTITUTION: The outside drawing of the product observing from each direction in three-dimensional space is generated in an interactive format by a design means 7 according to the input of a designer, and a design product is disassembled to each unit by a unit component developing means 8. The outside drawing of the unit is generated again at the design means 7, and each unit is disassembled to each component by the unit component developing means 8. Also, assembling sequence to assemble each unit from disassembled components is decided at a unit component assembling means 9 according to an assembling sequence decision rule, and also, it is decided according to the same rule to assemble the components from the disassembled units.