PURPOSE: To provide the method and system for component input for CAD for construction which facilitate input operation, enable short-time input specifying operation, and prevent misinput.

CONSTITUTION: The component input system 10 for CAD for construction is constituted by providing a master component storage means 21, a slave component storage means 22, a relative information storage means 23 which previously stores relative information between optional master components and slave components that are usable for the master components, a master component specifying means 30 which specifies necessary master components among the master components, a slave component automatic selecting means 40 which automatically selects only the slave components usable for the specified master components on the basis of the relative information, and a slave component specifying means 50 which specifies slave components out of the selected slave components.