There is provided a design support system including a designer terminal, a maintenance personnel terminal, and a design support device, in which the design support device includes a failure causal model database, a failure causal model updating unit that updates the failure causal model based on an assumed cause of a failure of the input target equipment, a maintenance support unit that estimates a type of a failure having a high occurrence probability and the cause thereof based on a symptom of the input target equipment and the failure causal model, and outputs the estimated result to the maintenance personnel terminal, a maintenance record database that stores authenticity information input from the maintenance personnel terminal for the estimated type of the failure and the cause, and a failure cause analysis unit that updates the failure causal model based on the authenticity information stored in the maintenance record database, estimates a failure cause of the target equipment based on the updated failure causal model, and outputs the estimated result to the designer terminal.