A software component reuse support method for supporting the use of existing software components when control software to be developed is created, using a specification database that stores the specifications of an existing device, a software component database that stores software components used in the control software of the existing device and the versions of the software components, and a computer, characterized by comprising: a likelihood analyzing step for calculating a likelihood P(A|B), said likelihood P(A||B) indicates the distribution of the frequency of use of each specification for each version of the software component, wherein said likelihood P(A||B) is calculated on the basis of said specifications of the device stored in the specification database, and the software components and the versions of the software components stored in the software component database; a prior probability analyzing step for calculating a prior probability P, said prior probability P indicates the distribution of the frequency of use of each version for each software component, wherein said prior probability P is calculated on the basis of the specifications of the device stored in the specification database and the software components and the versions of the software components stored in the software component database; a specification input step for inputting the specifications of a device to be developed; and a posterior probability analyzing step for calculating a posterior probability P(B|A), the posterior probability P(B|A) indicates the reusability of each version of the existing software component for each specification of the device to be developed, wherein, in the posterior probability calculating step the posterior probability is calculated by an expression P(B|A) = P(A||B) P /P, with the likelihood P(A|B), the prior probability P, the posterior probability P(B|A), and the probability that the specifications of the device to be developed will be selected from all the existing devices P. a likelihood analyzing step for calculating a likelihood P(A|B), said likelihood P(A||B) indicates the distribution of the frequency of use of each specification for each version of the software component, wherein said likelihood P(A||B) is calculated on the basis of said specifications of the device stored in the specification database, and the software components and the versions of the software components stored in the software component database; a prior probability analyzing step for calculating a prior probability P, said prior probability P indicates the distribution of the frequency of use of each version for each software component, wherein said prior probability P is calculated on the basis of the specifications of the device stored in the specification database and the software components and the versions of the software components stored in the software component database; a specification input step for inputting the specifications of a device to be developed; and a posterior probability analyzing step for calculating a posterior probability P(B|A), the posterior probability P(B|A) indicates the reusability of each version of the existing software component for each specification of the device to be developed, wherein, in the posterior probability calculating step the posterior probability is calculated by an expression P(B|A) = P(A||B) P /P, with the likelihood P(A|B), the prior probability P, the posterior probability P(B|A), and the probability that the specifications of the device to be developed will be selected from all the existing devices P.