The product design project includes many uncertainties. It causes risk that a project target cannot be accompolished within lead time. In order to flexibly handle the uncertainty and avoid the risk, adaptive planning that can switch easily to another plan by preparing options for a task is needed. When a challenging design alternative is difficult to be accompolished, a project manager should decide either to continue the design taking a risk or to switch to a conservative alternative disliking a risk. This paper proposes a new optimization-based project planning method that aims at a Pareto-optimal of the potential technical performane of designed product and a project failure risk. A task option model is employed for risk assesment of option-based project management. As its planning includes a number of various design variables and various evaluation indices, in order to solve such a complicated problem with a reasonable computation cost, this research separates the optimization problem into two phases, i.e., (i) defining of process architecture and organization structure and (ii) scheduling of resource allocation into activities. This paper demonstrates its application to a student formula design project. A proposed optimization method facilitates a project manager to explore various process plans with assessing their risks.