This paper introduces the function map, a directed graph containing “function nodes,” each of which consists of the description of a function, tasks, an implementation, and associated brain areas. A function is implemented when the implementation on the node accomplishes the tasks. To construct an AGI system, its overall functions must be decomposed to a large number of sub-functions. To facilitate decomposition, we propose a function map-driven development, in which a function map with a hierarchical structure is continuously constructed. This approach requires research and development to fill in incomplete function maps for continuous improvement. Upon the completion of the internal implementation of the top-level functions, the function map can be converted to a cognitive architecture representation. The map can also be converted to a roadmap for implementation of AGI by supplementing person-hours for the implementations that have yet to be realized.