A design/evaluation support tool 100 is constructed from a table link use unit 110 identifying linkages between a threat-to-component correspondence table 125, a risk-value table 126, a component contribution rate table 127, and a risk-to-assurance level correspondence table 128, based on their respective duplicate items; and a component assurance level deriving unit 111 deriving an assurance level of each of components that conforms to a risk value of a threat that a security function of each of the components counters by weighting the risk value of the threat by a component rate of contribution based on linkages of the tables.