A security-function-design support device is provided. The security-function-design support device includes a system-configuration data storage unit that stores information indicating a configuration of a system; an implementation-method storage unit that stores data indicating a security implementation method set for a configuring element of the system in order to implement a security function; an ancillary-function-element storage unit that stores data indicating an ancillary-function element set for the configuring element of the system in order to ensure a function of the security implementation method; an ancillary-function-element definition storage unit that stores a condition for determining a suitability of a setting of a given ancillary-function element; an ancillary-function-element evaluation unit that determines whether the ancillary-function element set for the configuring element of the system is suitable, on the basis of the condition for determining the suitability; and an evaluation-result output unit that outputs a result of the determination by the ancillary-function-element evaluation unit.